dimmer Dash Lights Work, but Dimmer Doesn't...

[NickyV]

Hey everybody! Just wanted to report that I was experiencing a problem that I know others have had. The issue was my dashboard/instrument cluster lights were working, but I wasn't able to dim them. As others have noted, this can be related to a malfunctioning headlight switch.

 

I fixed it by replacing the headlight switch.

 

Here are the symptoms I was experiencing:

 

- Dash/instrument lights would illuminate, but only when my headlight switch was rotated all the way to the left (counter clockwise). You know you've gone as far as you can go to the left when you hear/feel a click.

- When I rotated the headlight pull knob to the right (clockwise), I would lose all dash/instrument illumination as soon as the switch clicked going in the clockwise direction. The clock would also go out.

 

I went to the junkyard and grabbed a bunch of things, including two headlight switches. One was from a 1991 Cherokee (pictured top) and the other was from a 1988 Cherokee Laredo (pictured bottom). (I hope I'm remembering that correctly...) The switch that I ended up trying first was the bottom switch (the one that I believe came from the '88 Cherokee Laredo).

 

I mention the one I chose for a two reasons.

 

First, it just looked like it was in better condition, as you can see from the pictures. The ceramic wheel was not yellowing as much as the other one, and the terminals were a lot cleaner. If you have multiple switches to choose from, and don't have the know how or equipment to test them out, go with the equipment that looks better (at least that's what I say).

 

Second, after I pulled my busted switch out, I noticed that it looked a lot closer to the top switch in the picture I have attached. Specifically, it did not have the terminal prong that I have circled in the attached picture. I took a gamble and went with the switch that had an extra prong. I figured that it probably wouldn't hurt anything, and it might give me additional functionality in the long run. If anyone knows what the extra prong is for, I'd appreciate your answer in the comments section.

 

It's a bit of a pain to swap these out. I highly recommend removing the kickplate/lower dash. I think it would be possible to do without removing the lower dash, but you'd be working almost entirely blind. It's a whole lot easier to get out if you remove the instrument cluster as well, but I don't recommend doing that if you don't have to (especially if you've never removed the instrument cluster before). When removing the instrument cluster you have to be really careful, and it's very easy to accidentally mess up your speedometer cable.

 

Anyway, while I was at the junkyard, I also picked up some courtesy lights for the footwells. I am so happy I have these now! They illuminate when I open the driver's side door (but not the passenger door... perhaps that's by design, but I'm thinking that I need to do some more tinkering). They also light up when I turn the headlight knob all the way to the left (counter clockwise). And I'm hoping that when I get the time to tinker with the wiring in the pillar lights, that I'll be able to get those to light up when I open the door, but that's a project for another weekend. If anyone knows why my courtesy lights might not be lighting up when I open the passenger door, I'm all ears!

 

I'm including a video of a guy explaining how to remove it: 

 

 

 

[eaglescout526]

1 hour ago, NickyV said:

They illuminate when I open the driver's side door (but not the passenger door... perhaps that's by design, but I'm thinking that I need to do some more tinkering)

Check the switch in the door jamb itself. They corrode to where they wont conduct anymore and will need to be cleaned.

 

That being said. Highly recommend cleaning and adding grounds if you have not done this yet. And while we're talking about your headlamp switch, if you havent put your headlamps on a relay harness yet, we all recommend you should as that will reduce the power load on the switch itself. 

[Eagle_SX4]

5 hours ago, NickyV said:

dashboard/instrument cluster lights were working, but I wasn't able to dim them.

Not sure if you have replaced the bulbs in the instrument cluster or not, but most LED light bulbs are not dimmable. This could be your issue. Check what light bulbs you have installed in your cluster.

[schardein]

You mention the year of each headlight switch you got from the junkyard.  But you don't mention the year of your Comanche.  Put your vehicle information in your signature line, you can look at everyone's replies for examples.  This helps other forum members to help you.

 

Headlight switches are different for different years.  1984-1991 are different than 1992-2001.

That "extra" terminal on the bottom picture isn't used in Cherokees/Comanches.  If you look at the connector, there is no wire in that location.

The top switch is likely an original.  The bottom switch is probably a replacement.  The extra terminal serves a purpose in other applications that use the same switch, but not in the XJ/MJ.

 

The factory pillar lights will work the same as the under dash courtesy lights.  They come on when you open the doors.  Or by using the headlight switch (turn knob full CCW).   Or they can be switched on or off at the lights themselves.

 

When you replaced the headlight switch, hopefully you inspected the connector.  It's not uncommon to find the plastic melted and terminals burnt.  A new headlight switch might get things working, but is only half a fix if the connector/terminals are damaged as well.

[schardein]

And to answer your question about that unused terminal-

That terminal is power out for the parking lights circuit.  It is OFF when the light switch is off, ON when the parking lights are on, but OFF when the headlights are on.

Some older vehicles had front parking lights ON when parking lights were on, but OFF when the headlights were on.  My 1967 CJ5 was this way, stock.  I'm not sure the reasoning behind this, but my guess is it was to save a couple amps of power draw.  This was back when generators were still used, and even alternators were commonly rated at ~37 amps output.  Saving 1 to 1.5 amps from the front parking lights was probably worth it.

[NickyV]

Thanks to all who responded.

 

16 hours ago, eaglescout526 said:

Check the switch in the door jamb itself. They corrode to where they won't conduct anymore and will need to be cleaned.

 

That being said. Highly recommend cleaning and adding grounds if you have not done this yet. And while we're talking about your headlamp switch, if you havent put your headlamps on a relay harness yet, we all recommend you should as that will reduce the power load on the switch itself. 

 

 

@eaglescout526 Thanks! I guess I gotta get in there. Dang! I just finally put the floor kick plates back in after them being out for like three years. Oh well.

 

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12 hours ago, Eagle_SX4 said:

Not sure if you have replaced the bulbs in the instrument cluster or not, but most LED light bulbs are not dimmable. This could be your issue. Check what light bulbs you have installed in your cluster.

 

@Eagle_SX4 Good call. After replacing the switch, the dash is dimming as it should, but I'll keep that in mind in the future. Taking the instrument panel out is a pain and I really don't want to break my speedometer cable like I did last time!

 

But also good to note for others thinking about doing this swap. You might not want to do it if you have LEDs behind the dash?

 

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7 hours ago, schardein said:

Put your vehicle information in your signature line, you can look at everyone's replies for examples.  This helps other forum members to help you.

 

@schardein Good tip. I need to do that, and I will! And thanks for the intel on the extra prong on the headlight switch. Good to know.

 

7 hours ago, schardein said:

When you replaced the headlight switch, hopefully you inspected the connector.

 

Shoot. I did not. It was dark and I didn't get a good look at it. But I did read up on this a bunch before I made the swap and I think I understand what people are saying. My question is this: Think I can extend the life of the headlight switch by not dimming the dash lights? The way they are in my MJ, they aren't too bright. I don't mind having them at full brightness. I just wanted to have the feature because it was bugging me that it didn't work. And... as it turns out, I'm glad I did. Because if I hadn't then the footwell courtesy lights would be staying on 24/7, which I do not want, obviously!

 

Anyway, going forward, I am planning to keep the dimmer just to the right of the click.

 

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17 hours ago, eaglescout526 said:

And while we're talking about your headlamp switch, if you havent put your headlamps on a relay harness yet, we all recommend you should as that will reduce the power load on the switch itself. 

 

I definitely plan on getting one of those after market headlight harnesses as @eaglescout526 recommended. Seems like the move. I'm also excited by the prospect of not having to put LEDs in the headlights if I don't have to. I want my headlights to be a bit brighter. I don't live in an area with snow, but I prefer the look of the incandescents in the headlights. But I may want to go LED in the turn signals and brakes for safety purposes. What do you all think?

 

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4 hours ago, schardein said:

That terminal is power out for the parking lights circuit.

 

I see... But that won't impact my MJ? I have an 87 Base model, by the way. It sounds like what you are saying is that this will not impact my vehicle. I'll try to remember to look this evening.

 

 

BIG THANKS AGAIN TO ALL WHO ANSWERED + ANYONE WHO ANSWERS GOING FORWARD!

[schardein]

6 minutes ago, NickyV said:

 

I see... But that won't impact my MJ? I have an 87 Base model, by the way. It sounds like what you are saying is that this will not impact my vehicle. 

No impact at all.

[Eagle_SX4]

11 minutes ago, NickyV said:

 

But also good to note for others thinking about doing this swap. You might not want to do it if you have LEDs behind the dash?

The dimmer switch won't care what type of bulbs you have installed but just be aware if you do swap in LEDs they may not be dimmable and will be either on (with full or close to full voltage) or off (not sure what the cutoff voltage is but they will stop working before you get to 0 volts).

[schardein]

4 hours ago, NickyV said:

Think I can extend the life of the headlight switch by not dimming the dash lights?

I don't think the dash lights circuit is the real issue.  Dimming down the light probably does create more heat in the coil on the headlight switch, but not enough to cause problems with longevity.  Maybe others can chime in if they've had problems.

 

The real issue is the power for the headlights.  Here is the power flow- power comes from the battery, into the cab, through the headlight switch, through the high/low beam switch, back out of the cab into the engine compartment, and finally to the headlights.  All of the power for the headlights is going through the switch.

 

With the relay harness, power goes from the battery into the cab, to the headlight switch, to the high/low beam switch, back out into the engine compartment where it triggers the relays.  The relays draw maybe one amp.  That is a tiny load for the headlight switch.  Once the relay is triggered, power flows from the battery, to the relay, to the headlights.  That is a much shorter circuit to follow and results in less voltage drop as it reaches the headlights.

 

You get two great outcomes- less load on the headlight switch, and higher voltage at the headlights.

[NickyV]

13 hours ago, schardein said:

With the relay harness, power goes from the battery into the cab, to the headlight switch, to the high/low beam switch, back out into the engine compartment where it triggers the relays.  The relays draw maybe one amp.

 

Thanks for explaining that. Makes a ton of sense. I should get on that ASAP.

[NickyV]

One more question for @schardein or anyone else who cares to answer. There is this note on the K Suspension website about their version of the harness upgrade (for $25 this is well worth my time saved IMO).

Quote

 

**SPECIAL NOTE**

 

If you have a 97+ Jeep Cherokee XJ with FACTORY FOG LIGHTS. You MAY or MAY NOT run into the issue of your headlights not switching back to low beam after clicking on the High Beams and having to turn your lights off/on again for it to correct itself.

 

Is this something I need to be concerned about? I do have fog lights, but I'm pretty sure they were added by a PO, since the fog lights switch that came with it at time of purchase was not a factory switch and the slots for the switch are all blank.

[Eagle_SX4]

I have a k suspension headlight harness and it does work but could be better. The plugs for the headlights are ceramic but I don't think they were run through a kiln. They are crumbly. The relay included sometimes sticks and won't trigger. If you do end up getting one from them plan to use a different relay and to change out the headlight plugs.

[NickyV]

Thanks for the honest opinion, @Eagle_SX4. Do you have a recommendation for a similarly priced (or slightly more expensive) plug-and-play option? I know there are also diagrams of how to build one, which I could of course also do.

[Eagle_SX4]

I don't know of another h4 harness that cheap. Most of the other ones are about $100+.

 

[NickyV]

OK. Good to know!

[Eagle_SX4]

Jeepcables.com sells one built in the US for $95.50. I've heard good things about their battery cables.

 

https://www.jeepcables.com/products/daylight-headlight-harness

 

[GonzoTheGreat]

17 hours ago, Eagle_SX4 said:

Jeepcables.com sells one built in the US for $95.50. I've heard good things about their battery cables.

 

https://www.jeepcables.com/products/daylight-headlight-harness

 

I bought a jeepcables harness for my ‘89 and I was pleased with the quality.
 

If you really want to save a buck, I would opt to make it yourself over buying a cheap harness. You don’t want to compensate for inferior stock wiring with inferior aftermarket wiring. 

[AnotherOldJeepGuy]

I have the same dimmer issue.  Good info here.  I am really replying so I can get back here easily since I was not able to find how to select "follow topic" without posting some comment!  I guess since I am posting, I'll ask if anyone can recommend a good new replacement switch?

[eaglescout526]

50 minutes ago, AnotherOldJeepGuy said:

good new replacement switch?

I would definitely try to go OEM. Used or new. 

[gogmorgo]

I would stay away from used headlight switches myself, especially if you don’t have a relay harness installed. 
 

The issue with the headlight switches melting and catching fire is due to the switch arcing every time you make contact, and burning the contacts a little each time you switch it. This degrades the connection, and leads to increased resistance in the switch, which makes heat and decreases voltage available to your headlights. And sets things on fire. And back when my switch caught fire I dug through junkyards trying to find another connector and every single one I found was melted. I wouldn’t hold out much hope for finding a used switch that isn’t already on its way out.
This isn’t strictly the fault of the switch design, although it could be better, but with halogen bulbs you could be pulling 12-15 amps through it so it’s a pretty decent arc. LED headlights will cut that in half or better if you’re buying decent ones, but doesn’t completely fix the issue, and they may not always be happy getting reduced voltage through a scabby old switch. Especially if you’re buying junk LEDs off Amazon.
 

A relay harness shouldn’t interfere with factory fog lights. The way the circuit is set up the fog light switch only gets power from the low beam side of the dimmer switch, so the low beams have to be switched on to get power to the fog lights. If you’ve got aftermarket lights and/or custom wiring it’s anyone’s guess.

 

What a relay harness will interfere with is daytime running lights. It’s probably not a concern for most of you, because it’s not common for US trucks to have them, but DRLs were federally mandated in Canada for anything built or imported after ~1989. I can go into more detail there, including workarounds, if anyone wants, but I don’t want to muddy up this thread for no reason when it’s not relevant to the OP.