Factory fog light function

[schardein]

Not sure if this is a pub or tech section topic.  

 

I would like some input on factory fog light function.  I recently had a conversation on FB about factory fog lights.  We disagreed on how the fog lights work.  One thinks fog lights work with the parking lights on, and headlights off.  The other thinks the fog lights work only with the low beams on, and won't come on when the headlight switch is in the "parking lights" position.  We agree the fog lights are off when the high beams are switched on.

 

We both have wiring circuit diagrams that we think support our position.  We also both claim personal experience with factory fog lights that support our position.  Perhaps some years were different?

 

If you have factory fog lights, I would appreciate hearing your experience.  Can they be switched on when the parking lights are on?  Or must the headlight low beams be on to switch on the fog lights?

[acfortier]

My fog lights do not come on with parking lights on, and headlights off. I had this same thought a month ago and tried it. I had assumed they would work with parking lights on, and headlights off.

 

I didn't have fog lights from the factory but used the factory wiring from the cab to the main headlight harness, so I'm pretty sure the setup is the same (other than the normal headlight relay harness upgrade, which I also did).

[eaglescout526]

I did mine like it was from the factory. They work only when headlamps are actually on. They turn off when the brights are switched on and do not come on with just the marker lights. Kinda dumb to have fog lights on with markers. My wife’s 13 RAV4 is the same way. 

[gogmorgo]

Per the wiring diagrams I’m looking at in the FSM at XJJeeps.com, they’re tied to the low beam side of the dimmer switch. So they’ll only come on when the low beams are switched on.

There’s no power to the fog lamp switch without the low beams also getting power. Headlamps ON and switched to low beam. 

 

crappy highlighting of the relevant circuits brought to you by my thumbs and my phone.

 

Given this, it should not be possible to have the fogs switched on at any time the low beams are not also switched on. But considering how common it is to melt the headlight switch and associated wiring it wouldn’t surprise me if something in someone’s truck had been repaired incorrectly. Its also very possible someone didn’t like the way the fogs were wired and “corrected” it so they could be run without the low beams… I see people wanting to do that but in most cases if your low beams are glaring off the fog/snow at you they’re probably aimed wrong.

 

Legally speaking most jurisdictions only require that fog lights can’t be illuminated while the high beams are on, and the switch must be within reach of the driver. I think the idea is because you’re supposed to be using them instead of high beams, and probably switching them off when you meet oncoming traffic, like you would a high beam.

But double check local regulations before taking my word for it, some places have the legislation written such that they’re only to be on when the low beams are on. I’ve also never seen anyone talk about switching them off for oncoming traffic anywhere and can confirm no one ever actually does that when I’m driving towards them.

 

[ghetdjc320]

Same situation here. In my 91 they only worked with the headlight on and in low beam. Same goes for my TJ with factory fogs

[pizzaman09]

For a strange addition to this topic, I have found that with the fog light switch on, my fog lights also stay on with the sentinel light control that leaves the headlights on for 45 seconds after turning the car ignition.

[Ωhm]

50 minutes ago, pizzaman09 said:

For a strange addition to this topic, I have found that with the fog light switch on, my fog lights also stay on with the sentinel light control that leaves the headlights on for 45 seconds after turning the car ignition.

 

Funny you say that, because now I can see it in the wiring diagrams if Fog Lamp SW is ON and Dimmer SW is in LO. Headlamp SW can be ON, PARK or OFF, makes no difference. 

[schardein]

Thanks for all the input.  Yeah I was looking at the diagrams wondering if I was just dumb because there is no way the fog lights can be on without the low beams being on.  And same thing in actual experience.  I've modified my XJ so the fog light switch is standalone, but I know how it worked before the mod.  And my MJ has fog lights added, and I remember having to re-pin the harness because it was from a different year.  So the fact it only worked with the low beams on might have been because of something I did.  I'm relieved everyone is having the same conclusion.  With stock wiring, low beams must be on for the fog lamps to be on.

 

[Salvagedcircuit]

On a bit of a fog light tangent, does anyone know why the fog lights were changed from bring mounted on top of the bumper to a below the bumper on the cherokee XJ 97+? Was there a visibility benefit of putting the fog lights lower than the bumper?

I forsee a fog light installation in the near future and I might just have to test both positions and see for myself.

 

[eaglescout526]

Probably style. Keep the front grill area looking clean and hide the lamps under the bumper. If you look at cars from that era and up to now, you’ll see that they started putting them lower like that. 
 

[gogmorgo]

I would have guessed at it being due to cooling concerns and not wanting to block some of what was already a very small cooling area. But it’s definitely true that the trend was towards going lower and outwards 

[watchamakalit]

I think fog lights are supposed to be more effective the lower they are mounted. This may be the reason......

[75sv1]

The idea of fog lights is to beam light under the fog. Fog is a low level cloud. So, lower is better. I think it is against the law to have fog lights on when hi -beams are on. In Europe I think they have or had, where the fog lights would come on, but the headlights would come on dimmed. I've also hear this called "City light'. I can see this as an advantage. As sometimes in snow, fog or even rain, I get some glare .

[schardein]

That's my understanding.  Fog lights are intended to get under the fog, so the lower mounting is better.  I've also heard the purpose of amber or yellow lenses on fog lights is to make the vehicle more visible to other drivers.  It seems most modern vehicles don't bother with that.

 

Personally, I don't find fog lights useful.  Heavy fog is something I rarely encounter. The fog lights on my newer Silverado are barely discernible.  When switched on, I see a small amount of added light very close in and at the outside edges of the low beams.  Perhaps they would be more noticeable/useful when actually used in heavy fog?  I don't know.

 

I do like having a pair of driving lights. With a worn out set of original sealed beams or stock halogen headlights, having another set of driving lights aimed more or less where the low beams are can make a noticeable difference.  The set I have now is aimed just a little further out, between the low and high beams.  

 

After careful thought, I do believe it makes a lot more sense to upgrade headlights before adding other lights.  It's better to take advantage of the existing mounts, wiring (upgraded), and switch first.

 

But I'm off topic.  If anyone has ever encountered an XJ or MJ with fog lights that could be switched on with only the parking lights on, please chime in.  I don't think they were ever wired that way stock.

[87 MJ Chief]

If one of y'all will send me a set of factory fog lights, I'll slap those suckers right on G's Chief and let ya know how they operate on an '87 

[Eagle]

11 hours ago, 75sv1 said:

The idea of fog lights is to beam light under the fog. Fog is a low level cloud. So, lower is better.

 

Correct.

 

Quote

I think it is against the law to have fog lights on when hi -beams are on.

 

Also correct.

 

Quote

In Europe I think they have or had, where the fog lights would come on, but the headlights would come on dimmed. I've also hear this called "City light'.

 

I know many European cars have a "city light" that considerably less bright than regular headlights, but I have never heard that the city lights only function with fog lights.

[Eagle]

8 hours ago, schardein said:

But I'm off topic.  If anyone has ever encountered an XJ or MJ with fog lights that could be switched on with only the parking lights on, please chime in.  I don't think they were ever wired that way stock.

 

Late model XJs with factory fogs operate with only the parking lights on. Which is the way it should be. The way the Jeep factory did it in the 80s and early 90s, with the fogs only operable when the low beams are on, was stupid.

[schardein]

26 minutes ago, Eagle said:

 

Late model XJs with factory fogs operate with only the parking lights on. Which is the way it should be. The way the Jeep factory did it in the 80s and early 90s, with the fogs only operable when the low beams are on, was stupid.

So I was going to post, it turns out the person I was talking to, and I, were both right/wrong.

I kept researching, and it turns out 95-96 XJs had fog lights that could be turned on with the parking lights on.  I looks to me like the change happened with the change from the Saginaw steering column to the Chrysler airbag column.  The 95/96 XJs have a "parking light relay" and a "high beams relay".  I've printed the circuit pages from the FSM and it's a little hard for me to wrap my head around it, but it appears the fog light switch controls the ground for the parking light relay coil, and power flows from the parking light relay, through the normally closed side of the high beam relay to the fog lights.

 

And I agree, while the way they chose to wire it is strange to me, the function is better than only on with the low beams.

[75sv1]

I don't like the idea of parking lights only. I don't think it is enough light in driving situations. Also, other drivers expect seeing head lights. So, I do see the 'need' for City Lights. I think City Light are mainly used in Cities, as street lamps would provide much of the lighting. 

[gogmorgo]

Yeah, the idea behind the city lights is the street lighting provides enough lighting to see where you’re going. A lot of reflector housings have a small low-wattage bulb tucked in the side just to illuminate it so it looks like headlights to other road users, but you’re not shining headlights into windows or dazzling pedestrians or anything like that.

 

I agree on not running fogs on their own. If your low beams are glaring back at you they’re probably aimed a touch high. Unless you’re running ECE lights – that annoying kick up to the right for illuminating road signs is problematic, to say the least. 

[75sv1]

There are bracket from IRO that go on the steering knuckles. I have a set, but need to find lights that work with them. It would put them very low.

[gogmorgo]

18 minutes ago, 75sv1 said:

There are bracket from IRO that go on the steering knuckles. I have a set, but need to find lights that work with them. It would put them very low.

 

Nice and tucked up out of the way, so you wouldn’t hit anything with it. Just what you need for illuminating the inside of your bumper. I think you’d need a fair bit of lift to make that work. Could be useful to have the light follow your steering. 

[Eagle]

On 1/8/2024 at 11:29 AM, eaglescout526 said:

I did mine like it was from the factory. They work only when headlamps are actually on. They turn off when the brights are switched on and do not come on with just the marker lights. Kinda dumb to have fog lights on with markers. My wife’s 13 RAV4 is the same way. 

 

Not dumb at all. I imagine you never get fog in Arizona. Even low beam headlights can reflect back enough in heavy fog to be more effective at obscuring the road than illuminating it. That's why fog lights are ideally placed as low as possible and have a very flat cut-off. What's dumb is having fog lights that DON'T work with only the parking lights.

[eaglescout526]

No we don’t, but the state has switched to LEDs for all the street lamps and they suck enough to where I feel we need the extra lighting on when driving around. But I redact my statement prior though. That being said, if they’re supposed to come on with the marker lights especially on newer cars, then why the hell does my wife’s 13 RAV4 fog lamps come on only with the head lights? It’s like the XJ and MJ in this case. 

[gogmorgo]

I kinda wonder if the redesign was intended to reduce load on the headlight switch? The regulation is that they’re not to come on with the high beams, no specific requirement to only come on with the low beams, so coming on with the marker lights fits the bill, given you can’t really run your headlights without them anyhow. But it’s less wiring to just run them off the low beam circuit than to run off somewhere else and disable them with the high beams, provided everything in the circuit is up to task. Although the early XJ/MJ did have a fog light relay, so I don’t know how much the extra load of one relay matters to the switch… but I wasn’t in the engineering studio. 
 

We deal with blowing snow and ice fog up here, regular fog as well. The frozen stuff is a lot more reflective than the liquid. And I’ll reiterate that if your low beams are blinding you in fog they’re probably aimed a little too high.