Headlight harness relay upgrade... with DRLs?

[gogmorgo]

So this is probably one of those dumb wild goose chases that’s going to go nowhere, but it may prove useful for a handful of us in the long-term.

Can anyone think of a reasonably simple way that involves reasonably inexpensive, reliable, and easily sourced off-the-shelf components, that takes a single input (the high beam pin at the socket), can tell whether it’s receiving nominally 5 or 12V, and accordingly put the 5V straight through to the high beam filament, but when it receives 12V triggers a relay to deliver battery voltage? (And also stays off when receiving no voltage?) I’m pretty good with switches and relays, and can wrap my head around resistors and diodes, but this is beyond my skill set.

 

Where this comes from is that daytime running lights are a legal requirement on all vehicles sold new in Canada after Dec 1, 1989. As we know, the factory headlight wiring on the xj/mj is maybe a little less than optimal, and most of us make up for it with the relay harness which supposedly retains all factory functions. Thing is, the relay harness doesn’t play well with the DRLs.

The function of the DRL is that the module sends 5V to the high beam filaments when the vehicle is moving. The result when paired with a relay harness, depending on the relays used, is either:

•5V isn’t enough to trigger the relays, so you have no DRL; or

•You have high beams on full beam whenever the vehicle is in motion and you don’t have the low beams on.

In my case, it’s the former, but I’ve definitely encountered other vehicles on the road running full beam high beams and no other lights in the middle of the day. To avoid the albeit minuscule risk of being pulled over for no DRL, or the risk of running full high beams everywhere, I’ve always just driven with the low beams on. But at some point in the future I will be faced with an inspection before I can register my long bed, and pretending won’t be good enough for that. Returning to stock for the inspection is the obvious answer, except that when I built my relay harness i found my headlight harness was in such poor shape that it became more a matter of building a new headlight harness with added relays than it was adding a supplementary harness... so going back to stock isn’t going to be quite as simple as unplugging the supplementary harness and plugging factory sockets back in. It would also be nice to be able to be able to recommend the relay harness to fellow Canadians as an upgrade without having to add the caveat that a side effect of preventing setting your truck on fire is that it’ll no longer be compliant with CMVSS lighting requirements, and that they may need to take extra steps or even undo it from time to time to make it look compliant.

The second obvious answer is to ditch the factory DRL module and just add a couple relays to run either the parking light or low beam circuits whenever the key is on. This is actually how they added DRLs “at the port” to Canadian-spec Ladas. However now you’re tapping into additional circuits on the vehicle, and moving away from the spirit of a simple plug and play supplementary harness upgrade. And also interfering with my personal perversion for maintaining original functionality whenever possible.

 

So to that end, can anyone help with this?

[omega_rugal]

some relays have 2 outputs, normally closed and normally open, run 5v through the NC wire and 12v throught the NO wire, by powering the solenoid you can toggle between 5v and 12 v

 

either that i don't get the idea...

[omega_rugal]

Or you can use a zener diode...

[Tex06]

I've got a '92 with stock headlight harness.....so you're telling me that it should have automatic DRL? I.e. Key is on and my headlamps light up partially?

 

My truck was purchased with California spec emissions (I just found that out) so I assume it would have Cali-spec electronics too.

[jdog]

43 minutes ago, Tex06 said:

I've got a '92 with stock headlight harness.....so you're telling me that it should have automatic DRL? I.e. Key is on and my headlamps light up partially?

 

My truck was purchased with California spec emissions (I just found that out) so I assume it would have Cali-spec electronics too.

Nope only if it went to Canada, even then it sounds like it didn't and he's trying to figure out how to get them to be on

[gogmorgo]

6 hours ago, omega_rugal said:

some relays have 2 outputs, normally closed and normally open, run 5v through the NC wire and 12v throught the NO wire, by powering the solenoid you can toggle between 5v and 12 v

 

either that i don't get the idea...

Basically I need the 5V to toggle the 5V going through to the light, and the 12V to toggle the 12V, but coming from the same wire and going to the same wire, but pulling the 12V from another source.

This is kinda the direction I was thinking, using the no/nc pins.
If you took a standard automotive relay:

You’d have 87A hooked to the truck’s headlight socket high beam, and 30 going to the harness’s high beam socket. 87 goes to battery. Switching then becomes the obstacle.

If you can guarantee the relay won’t switch with 5V, all you’d need to do is ground 86 and tie 85 to 87A, but to foolproof it you’d want a zener diode in there, probably with a breakdown voltage in the range of six to eight volts.

 

That last part is where my talent runs out. I don’t know how to spec and source a zener diode that will work. I guess I should’ve included that in my original post. I don’t have good access to an electronics store, and the online suppliers have so many diodes that it’s overwhelming trying to sift through tens of thousands of results to find one that would work, even if I’m not looking for perfect, just something that does what I want.

I also got stuck somehow thinking that the above setup would leave the lights on when the truck is off or with the low beams, and only just realized while writing that out that when the high beams are seeing 0V, so would everything else involved, so I guess that’s a non-issue.

I know that it would probably work without the zener diode in there, given the relays I bought for my harness won’t switch with 5V, but I want to be able to have a write-up that is guaranteed to work no matter what relay gets sourced by the person involved. I also don’t want to run the risk of a relay that doesn’t switch with 5V having its spring weaken over time and then start switching with no one realizing except oncoming traffic. It’s better not to rely on the accidental functions of a device, at least in my mind.

[gogmorgo]

3 hours ago, Tex06 said:

I've got a '92 with stock headlight harness.....so you're telling me that it should have automatic DRL? I.e. Key is on and my headlamps light up partially?

 

My truck was purchased with California spec emissions (I just found that out) so I assume it would have Cali-spec electronics too.

Only if it’s “Canada-spec”. A bit further north than California.

Daytime running lights were an option on US-market vehicles, but probably unlikely. I don’t honestly know if they are a requirement in any jurisdiction outside of Canada.

[Fernando87mj]

This might help , hornbrod (rip) always had some neat stuff going on 

 

[gogmorgo]

6 minutes ago, Fernando87mj said:

This might help , hornbrod (rip) always had some neat stuff going on 

 

Not really the same thing.

Also, as much as I respect Don’s memory, I really have to disagree with his comments on this thread in regards to European headlights. I just bought some new DOT housings for my ZJ to replace the ECE lights I put in a couple years ago. They have their advantages, but I’m getting pretty sick of not being able to see much of anything with the low beams.

[scguy]

This is more complicated, but you could make a plug and play headlight relay harness that uses 3 relays to put the headlights in series, so they would run at ~6V each.

The attached diagram is for fans, but it would work for headlights.

[Tex06]

This might help:

 

 https://www.rockauto.com/en/moreinfo.php?pk=1534384&cc=1181821&jsn=70299

 

$62 plus the ride for the OEM part.

[gogmorgo]

13 minutes ago, Tex06 said:

This might help:

 

 https://www.rockauto.com/en/moreinfo.php?pk=1534384&cc=1181821&jsn=70299

 

$62 plus the ride for the OEM part.

For someone wanting to add DRL to an MJ that doesn’t already have them, maybe. But both my MJs already have them. I’m trying to build a supplementary relay harness that won’t disable them.

[Tex06]

25 minutes ago, gogmorgo said:

For someone wanting to add DRL to an MJ that doesn’t already have them, maybe. But both my MJs already have them. I’m trying to build a supplementary relay harness that won’t disable them.

Ahhhhh. Now it all makes sense. 

 

A couple of ideas that don't answer your question: 

 

1. Upgrade to LED lights and use the stock wiring harness. No high amp draw so no supplementary relay needed.

 

2. IIRC, the weak point in the OEM circuit is the wire and grounding. Cut out the stock wire (I believe it's 14 gauge aluminum) and replace with 12 gauge copper. Add in an extra ground for the driver's side light.  EDIT: Saw you had basically already done this but with the relays hardwired in. What size wire did you go back with?

 

Both of these limit extra wiring and connections under the hood which is usually a good thing. One is cheap but takes time, the other is quick but more $$$. 

[gogmorgo]

1. LED headlights are trash. They REALLY don’t play nice with DRL, either.

2. The weakest point is the switch itself. The high load with the switch on the positive side of the circuit leads to arcing and burnt contacts, burnt contacts conduct poorly and get HOT. If the switch was on the ground side, it would last a lot longer as voltage is much lower after the headlights so it won’t arc as much. Poor grounds are crappy and will make your lights dim, but they won’t set your truck on fire.

I used 14awg for the switching curcuit of my harness, but only as far as the factory connector. Load side is 10awg. The wires on the truck side of the connector weren’t in bad shape so I spliced in to them. It wouldn’t be that big a deal to go back to factory. All it would take is finding another harness and connector, which I’m pretty sure I already have in my parts hoard. Mostly it’s just that I don’t want to go to the trouble of doing it just to undo it again after the inspection to make it non-compliant. I’d rather just deal with it once. Driving around in a non-compliant vehicle also isn’t a great look for me, professionally.

[Tex06]

Fair enough. I've got my eyes on a set of trucklites after driving a buddies XJ with them. My 2019 Africa Twin also has LEDs. 

The eBay stuff that looks like an egg crate? Trash.

 

What about running a relay in parallel on the high beam side? The 5VDC would feed straight to the DRL and then when the 12VDC came in, it would trip the relay into working and split the amperage between the relay and the OEM circuit. Not ideal, but it would work, be an easy plug&play, and not break the bank.

[gogmorgo]

1 hour ago, Tex06 said:

What about running a relay in parallel on the high beam side? The 5VDC would feed straight to the DRL and then when the 12VDC came in, it would trip the relay into working and split the amperage between the relay and the OEM circuit. Not ideal, but it would work, be an easy plug&play, and not break the bank.

That’s basically the idea I think. I’ll have to put together a circuit diagram tonight. I’d like to get a zener diode in there though to absolutely guarantee  the relay won’t trigger on 5V. I could also probably put a resistor in to knock down the voltage to below triggering voltage on the relay, but that’s a bit messier of a solution in my mind. My only hold-up at this point is I don’t know where to start sourcing a zener diode... go to a place like Mouser, and you get 50,000 results ranging in cost from fractions of cents to hundreds of dollars, and I really have no idea what I’m looking for.

 

I feel I need to explain my aversion to LED headlights. I’ve never been happy in a vehicle with them. It’s as if they’re too bright. You meet them oncoming and you lose all night vision. In the vehicle, you can’t see anything where they’re not illuminating. The better ones are brighter and more focused with better cutoffs, but that almost makes it worse. They’re totally okay if you live somewhere well-illuminated, but I live in a national park that also happens to be the world’s second largest dark-sky preserve. When it’s overcast at night, you can barely even see your hand in front of your face. I’ve got two vehicles running e-codes, and it’s the same issue. I don’t even catch eye shine outside of my beams, which is an issue with these guys running around all over the place:

 

(this was just now, across the street from my house)

I also finally got the ecodes on my zj aimed to where I’m not getting flashed by oncoming traffic or blinding myself with the glare off street signs, and now I can’t see far enough down the road for the low beams to be useful. I had to drive ~100 miles in a snowstorm a couple weeks ago, and it was pretty brutal... can’t run high beams in the snow, can’t see far enough with low beams, so now it’s going back to stock SAE headlights. I also can’t see much going around tight corners or through dips, which we have a few of in the mountains here.

LEDs also don’t like getting the 5V from the DRL module. Most people report them flickering pretty badly until they switch on headlights. 
The stock sealed beams on my MJs, even without the relay harness, may seem pretty dim in contrast (especially without the relay harness), to ecodes or LED lights, but I can still actually see everything I need to, which is much more important in my mind. At least, I can see everything up until I meet someone oncoming with cheap, badly focussed, poorly aimed LED lights...

[gogmorgo]

Digging into zener diodes a bit more, I’m no longer entirely convinced it’s the way to go.

What it looks like is that yes, they will block voltage below the reverse breakdown voltage, but it also looks like they will also have a reasonably consistent voltage drop of that same voltage. So, say you put one with a breakdown voltage of 6V in series with the control circuit of a relay, it won’t allow current to pass through until the voltage across it hits 6V, but in the 13.5V circuit, that leaves 7.5V to trigger the relay. This could feasibly happen given I’ve seen reports of 12V relays switching with as little as 4V, but all reports indicate you want at least 9V on your switch circuit to ensure reliability.

The other obstacle is now that I’ve figured out how to filter the search results on Mouser, (seriously, @#$% defaulting to low-feature mobile sites) is that it seems most of the options are for relatively low-power circuits, PCBs and such, so there are very few options that will hold the current necessary to operate an automotive relay. On the other hand, it makes choosing something easier.
 

It should however be possible to use a 6V automotive relay coupled with a ~6.5V 3W Zener diode. Current would be blocked with the DRL on 5V, but once it jumps up to full nominal 12V high beam, you’d still have ~7V to reliably switch the 6V relay. And given the 6V relay will only be switching another relay and not really carrying substantial load, I don’t anticipate running 12V through the load circuit would cause any problems. Except there’s a little bit of doubt there, especially considering half the point of the relay harness is to stop the truck from catching fire...

[Tex06]

9 hours ago, gogmorgo said:

Digging into zener diodes a bit more, I’m no longer entirely convinced it’s the way to go.

What it looks like is that yes, they will block voltage below the reverse breakdown voltage, but it also looks like they will also have a reasonably consistent voltage drop of that same voltage. So, say you put one with a breakdown voltage of 6V in series with the control circuit of a relay, it won’t allow current to pass through until the voltage across it hits 6V, but in the 13.5V circuit, that leaves 7.5V to trigger the relay. This could feasibly happen given I’ve seen reports of 12V relays switching with as little as 4V, but all reports indicate you want at least 9V on your switch circuit to ensure reliability.

The other obstacle is now that I’ve figured out how to filter the search results on Mouser, (seriously, @#$% defaulting to low-feature mobile sites) is that it seems most of the options are for relatively low-power circuits, PCBs and such, so there are very few options that will hold the current necessary to operate an automotive relay. On the other hand, it makes choosing something easier.
 

It should however be possible to use a 6V automotive relay coupled with a ~6.5V 3W Zener diode. Current would be blocked with the DRL on 5V, but once it jumps up to full nominal 12V high beam, you’d still have ~7V to reliably switch the 6V relay. And given the 6V relay will only be switching another relay and not really carrying substantial load, I don’t anticipate running 12V through the load circuit would cause any problems. Except there’s a little bit of doubt there, especially considering half the point of the relay harness is to stop the truck from catching fire...

 

Yeah, after reading your previous post, I was curious why you were so bent on a Zener....

I use digikey to spec out a lot of my electronic parts, even if I don't purchase from them, their website is easy to use and read. Their automotive relays have a column of "must operate voltage"....I'd guess that if you got one that was >10% above whatever your 5VDC actually is you'd be fine. I'd personally grab something that MOV is around 7VDC, slap it in and forget about it.

 

Here's one that would work but is way overkill. It's Must Operate is 8VDC and Must Release is 4VDC. Assuming you're at 5VDC +/-10%, this would work.....it's just rated for 75A, lol. Dig around and see what you can find, relays are cheap so if one doesn't work the way you think it should, swap it. A lot of these you can find on Amazon or eBay too, I just spec them with digikey.

https://www.digikey.com/en/products/detail/te-connectivity-potter-brumfield-relays/1904001-2/3466302

[derf]

Is it possible to separate the DRL controller at the source and just run a different wire to the relay harness?  It might take some more digging to do that but if you can isolate it so that the headlight switch just controls the normal lights and then have the DRL trigger run through a different relay, would that simplify things a bit?

[gogmorgo]

10 minutes ago, Tex06 said:

 

Yeah, after reading your previous post, I was curious why you were so bent on a Zener....

I’ve never studied electronics. Basic level electrical physics before I dropped out of university, but we didn’t play around with anything much more than lightbulbs and other resistors. Going through mechanic classes they introduced us to a bunch of components, but we didn’t go very in depth on actual circuit design. Learning to measure breakdown voltage of the zener was about it, and we definitely didn’t see them used for what I was trying to do. I was kinda wondering about using a zener initially, so then when Omega suggested it so quickly I kinda jumped on it, cause that’s what I was already wanting to do.

I’ll have to dig into relay choice a bit more I guess. I still would like to be able to walk into any parts store anywhere and grab an off-the-shelf component if the relay ever fails, which is why it would be nice to have some sort of voltage blocker in place. Using a simple off-the-shelf resistor to bump the voltage down a bit would work, but with variability of parts-store relays it might be interesting choosing a resistance that works with most of the relays out there.

I’m also not excited about a hold-in voltage below 5V, given on the off chance the head lights are switched off with high beams on, then the DRL voltage might be enough to keep the relay latched so you’ll just have high beams on full up until you either shut the truck off or turn the low beams back on... Correct?

 

 

20 minutes ago, derf said:

Is it possible to separate the DRL controller at the source and just run a different wire to the relay harness?  It might take some more digging to do that but if you can isolate it so that the headlight switch just controls the normal lights and then have the DRL trigger run through a different relay, would that simplify things a bit?

I’m still kinda hoping to keep it as a supplemental harness, with the same idea as the “regular” relay harness, something you just add in between your headlights and their sockets, without having to splice into other harnesses just to make it work. The more complicated you make the thing, the less likely anyone’s ever going to choose to use it over having a simple but non-compliant vehicle and “just turn on the low beams”. I really would like to be able to say “build this very basic relay circuit, attach these to battery and these to your headlight sockets and plug in your bulbs”, same as the original.

[derf]

20 minutes ago, gogmorgo said:

I’m still kinda hoping to keep it as a supplemental harness, with the same idea as the “regular” relay harness, something you just add in between your headlights and their sockets, without having to splice into other harnesses just to make it work. The more complicated you make the thing, the less likely anyone’s ever going to choose to use it over having a simple but non-compliant vehicle and “just turn on the low beams”. I really would like to be able to say “build this very basic relay circuit, attach these to battery and these to your headlight sockets and plug in your bulbs”, same as the original.
 

Ok, I can see that.

 

Is it possible to tap a "hot in run" trigger somewhere?  You could use that to drive a DRL relay that switches a 5v supply to the headlight (maybe integrate a step down circuit tapped to battery+ to supply to the light).  Add in a second (normally closed) relay that would cut power when the low beams are turned on.

 

You'd have a self contained harness that just has one extra wire you have to route somewhere else and tap it in.

[Ωhm]

Does the DRLM know when the headlight switch (LO/HI) is ON?

[derf]

Maybe a cheap little arduino could read the incoming voltages and trigger relays for the lights...

[Tex06]

1 hour ago, derf said:

Maybe a cheap little arduino could read the incoming voltages and trigger relays for the lights...

I'm gonna be the first to veto this idea. Arduinos are very cool, very powerful little devices but one thing they are not is reliable. I've had to go back and "undo" several things where some enterprising individual scabbed in an arduino in a place where a proper PLC should have been and then they can't figure out why things go to dookie-doo when it crashes and has to be restarted. They are one of my #1 headaches when improperly used. (but if you want to try it, don't let me stop ya!)

[gogmorgo]

Some circuit diagrams so we’re all on the same page:

 

I’m sure we can all agree this is what a basic supplemental relay harness looks like:

The power that the factory used to illuminate the headlights is now being used only to trigger a pair of relays that unload the vehicle circuits. Ideally you’d really want ground-side switching to reduce arcing and extend the life of the relays, but the circuit works reliably enough, and while I did lose one of my relays, it was a used one I pulled at a junkyard anyhow so I can’t really blame the circuit on it.

 

This is the proposed addition to allow for DRL that function as set up by the factory:

With key on (truck in motion) and headlights off, the truck’s high beam circuit will see 5V. The DRL relay in the normally closed position will allow that 5V to flow through it and directly to the high beam circuit.

With the low beams are switched on, the high beam circuit and DRL relay will see 0V, so no the normally closed relay will send 0V through to the high beam circuit and they won’t come on.

Once the high beams are switched on, the DRL relay will see 12V from the truck’s high beam circuit, and switch the DRL relay, which will then in turn send the 12V through to the high beam relay, triggering it to switch on the headlights.

 

I like this circuit. It’s simple, low cost, parts are readily available, and it would be easy for someone with a very basic knowledge of vehicle electrical systems to build and install, much like the basic relay harnesses most of us use.

The big glaring issue with this circuit design is that you need the DRL relay that absolutely will not trigger with 5V, and that will absolutely release if for some reason the headlights are switched off while the high beams are on (and voltage to the DRL relay drops from 12 to 5V instead of to 0V like if you were just to switch from high to low beam).

It would be nice to have some sort of voltage blocker in the starred circuit to stop the DRL relay from triggering at DRL voltage, which is what my hangup is. I know that most relays won’t trigger with 5V, but some will and it would be nice to guarantee it won’t happen somehow.

1 hour ago, Ωhm said:

Does the DRLM know when the headlight switch (LO/HI) is ON?

Yes. As soon as you turn on the headlights with the dash switch, the DRL module stops doing it’s thing. IIRC it might get its signal from the dimmer (high beam/low beam) switch somehow, but I’d have to go back to the circuit diagram. The DRL module is also in communication with a bunch of stuff. I don’t remember how it operates on my automatic, but on my manual MJ it won’t actually turn on until the vehicle starts moving. I had to lift the rear axle off the ground and put it in gear before I could actually measure anything.

But I’d like to eliminate vehicle-specific wiring as a variable.

2 hours ago, derf said:

Ok, I can see that.

 

Is it possible to tap a "hot in run" trigger somewhere?  You could use that to drive a DRL relay that switches a 5v supply to the headlight (maybe integrate a step down circuit tapped to battery+ to supply to the light).  Add in a second (normally closed) relay that would cut power when the low beams are turned on.

 

You'd have a self contained harness that just has one extra wire you have to route somewhere else and tap it in.

Part of what I’d like to achieve is a system that isn’t vehicle specific. The XJ/MJ share the same DRL module with the TJ, YJ, ZJ, and SJ. Lots of Chrysler vehicles use a very similar voltage step-down for their DRL circuits, and I’m pretty sure Ford does as well, unless they’re doing what a lot of Japanese manufacturers did back in the ‘90s and had a bunch of relays to switch the high beams to run in series, which comes with its own set of issues.

It’s also been suggested that I just use some relays to turn on low beams or parking lights, but again then we’re tapping into extra vehicle circuits.

 

1 hour ago, derf said:

Maybe a cheap little arduino could read the incoming voltages and trigger relays for the lights...

I’ve thought about this too, but this moves away from simple and easily reproducible by someone else with very basic understanding of vehicle electric systems and minimal equipment. I also don’t know what it would cost.

One of the other big advantages of the basic relay harness is that it’s a great beginner project for someone to learn how to start adding additional lighting circuits to a vehicle the proper way, and I feel like running an Arduino or similar isn’t necessarily the way to go there.