How to repair multifunction switch for fog lights (fog lights that won't turn off)

Since more than a few have asked, here is what I'll offer about relays, lighting, or whatever accessory you are trying to control.
This link is a great place to start if you know nothing about relays: (no affiliation)
https://www.onallcylinders.com/2015/01/02/relay-case-whys-hows-using-relays-automotive-wiring/

The short story is this:
If your fog lights remain on when the multi-function switch is in the OFF position, a relay will not solve the problem - UNLESS YOU ALSO REPLACE OR JUST BYPASS THE FAILED MFS.
What I mean by this is that the lights are staying on because the switch is not breaking contact and the reason is because of the tiny electrical contacts inside the switch have become corroded, gummed up, ETC. and can't disengage.

Jeep engineers SHOULD have put in relays at the factory, but they didn't and here we are.
This is a typical automotive-type relay circuit (although it says FAN & has a thermal switch, the circuit diagram is the same for lights, or other accessories such as a compressor, etc.).
1658532120559.png

The key to this circuit is to use a toggle-type switch to control the ground applied to pin 85.
The +12V ignition can basically come from any wire that is hot when the ignition is on.
It can piggy-back on almost any circuit, as the current draw here is not going to be for the accessory, only for the relay, which draws very little current.

The output from pion 87 goes to the red (hot wire) for the accessory. Ground the accessory using the black wire that is part of that harness.

The wire labeled above as BATTERY +12 (pin 30) is connected directly to the battery "+" post, or another unfused circuit that makes sense.

How it works:
When you flip your switch (connected to pin 85), that grounds the relay, which then energizes the coil inside it.
When the coil inside the relay is energized, it connects the +12V on pin 30 to the output on pin 87.

This means that your accessory is now powered from the following circuit: Direct battery, through pin 30, out pin 87 to your device.
This places only a very small current between the +12V ignition wire and your switch.

Pin 87a (if your relay is equipped), is always the opposite of pin 87.
Technically, 87 is called Normally Open & 87a is called Normally Closed.

Now you have asked, "Where to install the relay?"
In the Jeep TJ circuit, the best place to install the relay is between the MFS (or your new toggle switch) and the lights (where the MFS/toggle is the manual switch in the diagram above).

I fixed mine by chasing the fog light wire through the harness back to the MFS. I cut the wire and connected it to pin 87.
I added a rocker switch to my dash, and made the rest of the wiring harness.
This approach also allows me to keep the fog lights on when the high beams are engaged.
 
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Since more than a few have asked, here is what I'll offer about relays, lighting, or whatever accessory you are trying to control.
This link is a great place to start if you know nothing about relays: (no affiliation)
https://www.onallcylinders.com/2015/01/02/relay-case-whys-hows-using-relays-automotive-wiring/

The short story is this:
If your fog lights remain on when the multi-function switch is in the OFF position, a relay will not solve the problem - UNLESS YOU ALSO REPLACE OR JUST BYPASS THE FAILED MFS.
What I mean by this is that the lights are staying on because the switch is not breaking contact and the reason is because of the tiny electrical contacts inside the switch have become corroded, gummed up, ETC. and can't disengage.

Jeep engineers SHOULD have put in relays at the factory, but they didn't and here we are.
This is a typical automotive-type relay circuit (although it says FAN & has a thermal switch, the circuit diagram is the same for lights, or other accessories such as a compressor, etc.).
View attachment 345124
The key to this circuit is to use a toggle-type switch to control the ground applied to pin 85.
The +12V ignition can basically come from any wire that is hot when the ignition is on.
It can piggy-back on almost any circuit, as the current draw here is not going to be for the accessory, only for the relay, which draws very little current.

The output from pion 87 goes to the red (hot wire) for the accessory. Ground the accessory using the black wire that is part of that harness.

The wire labeled above as BATTERY +12 (pin 30) is connected directly to the battery "+" post, or another unfused circuit that makes sense.

How it works:
When you flip your switch (connected to pin 85), that grounds the relay, which then energizes the coil inside it.
When the coil inside the relay is energized, it connects the +12V on pin 30 to the output on pin 87.

This means that your accessory is now powered from the following circuit: Direct battery, through pin 30, out pin 87 to your device.
This places only a very small current between the +12V ignition wire and your switch.

Pin 87a (if your relay is equipped), is always the opposite of pin 87.
Technically, 87 is called Normally Open & 87a is called Normally Closed.

Now you have asked, "Where to install the relay?"
In the Jeep TJ circuit, the best place to install the relay is between the MFS (or your new toggle switch) and the lights (where the MFS/toggle is the manual switch in the diagram above).

I fixed mine by chasing the fog light wire through the harness back to the MFS. I cut the wire and connected it to pin 87.
I added a rocker switch to my dash, and made the rest of the wiring harness.
This approach also allows me to keep the fog lights on when the high beams are engaged.

much thanks... guess you would follow your suggestions above for headlight circuit too... which IMHO is the most important one to put a relay into cause it is used more often..... putting high juice thru the MFS more often..... though adding headlight relay would be little more complicated for I assume there is additional legs of that relay that are separate low beam and high beam...aka..... I assume a headlight relay is essentially two relays in one. PS- then again.... I do know how one spells... ass u me and I may well be assuming to much about how a headlight relay works.
 
If I were to add my own relay circuit for headlights, I would actually use (2) relays; one for lo beam & a 2nd one for high beam, but yes, the same general circuitry would apply.
 
I fixed my multi function switch and it was very easy to do. I modified it as well by filling in the “dimple” with JBweld and overlayed a very thin piece of aluminum into the concave surface, cut from a soda can, matched to the size of the concave surface.
 
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There's some pics a few pages back, but I used a piece of RC Cola can and and JB Weld. It worked good, but a few months later my multi-malfunction switch developed other issues with the turn signals involving some beeper in the dash and I caught a new OEM Mopar switch at a decent price so I just replaced it. Still got the old one in my parts stash "just in case".

I’m thinking of just replacing the entire thing with a rockauto multifunction switch. Last time I tore this down to fix it, I had to remove it 3 different times cause every time I put it back on the Jeep, some crazy stuff started happening. I remember once all the lights just kept flashing in the dash, the other times, some other weird stuff happened. Wiped out the old electrical grease and put new one on it and it seemed to fix it but I wouldn’t be surprised if the stuff is just corroded in there. My fix only lasted about a year or so and it’s melted again. It’s kind of annoying.
 
Thanks for the write up. Just did this repair and fixed the issues on my 02 Sahara. At first fog lights would come on after a turn signal was used and wouldn't turn off until I applied a little force to the end of the stalk. Then the right blinker no longer worked unless I applied a force to the end of the stalk while also holding it up to engage the right blinker. Did the fix and now right blinker works and fog lights don't come on unless actually switched on.
 
After I repaired mine I was still having issues with turn signals and a beeping in the dash. I decided to just spend the money for a new Mopar one which still didn't sort it out as it was doing the same thing. Eventually, I replaced the LED lights & flasher with stock type units and it's all worked like it should since. My old multifunction switch is good but is now a backup unit on a shelf in my shop.

Yeah, I don’t know if I should do that to my 04 or not. Just has LED headlights but I have been having this beeping in the dash and left blinker is solid but I can’t get a good enough connection on my left blinker. Took apart electric grease, attached, worked fine for a few minutes and then went back to the same thing. Bulb is not bad.
 
Here’s my take:
You said the LED lamp is good because it lights. Probably. Are the contacts worn or misaligned?
I had that issue with the taillights in my Charger. Bent the contact on the lamp and that solved it.

You’ve cleaned the contacts and added grease to prevent additional corrosion. Good move on a new socket, but this may be ineffective on an old/worn/corroded one.

All that’s probably left is to replace the socket itself.
These do wear out.

The next step I would take to confirm the failure mode as either “socket or source” would be to T-tap into the wiring and check the voltage & ground feeds going INTO the socket.

Or, just cut the wires close to the socket to give yourself the longest possible wiring after cutting that old socket off. 😉
 
Here’s my take:
You said the LED lamp is good because it lights. Probably. Are the contacts worn or misaligned?
I had that issue with the taillights in my Charger. Bent the contact on the lamp and that solved it.

You’ve cleaned the contacts and added grease to prevent additional corrosion. Good move on a new socket, but this may be ineffective on an old/worn/corroded one.

All that’s probably left is to replace the socket itself.
These do wear out.

The next step I would take to confirm the failure mode as either “socket or source” would be to T-tap into the wiring and check the voltage & ground feeds going INTO the socket.

Or, just cut the wires close to the socket to give yourself the longest possible wiring after cutting that old socket off. 😉

Good to know. I’ll start will a new socket-much cheaper lol. I know I keep falling with the socket and bulb and it’ll work and then it’ll quit then it’ll work and quit so I know it’s the connection and has to be the socket. That could be sending a signal back to the multifunction plug, maybe.
 
Here's an alternative write-up (though almost identical) to the one @bobthetj03 posted:

My 2003 Jeep Wrangler started magically turning on the fog lights while I had it parked. This issue kept getting worse until I could not get the lights to stay off without touching the switch. At first I was able to put my left turn signal on and this was just a temporary fix. I went to the dealer and they told me the switch would cost me $260 this is why I wanted to fix the existing switch. I want to keep my jeep nice and running another switch somewhere else would just bug me.

This write up includes removing the switch from the steering column.

Tools Needed
First you need to remove the steering the column plastic cover there are two screws in the holes closest to the steering wheel. Phillips

View attachment 10683

Now you can remove the two T20 screws on top of the multifunction switch. There are two harness plugs going into this switch which both have a red tab that need to be pulled out (but not completely) in order to be unplugged.

View attachment 10684

Now the entire switch assembly can be removed.

View attachment 10685

View attachment 10686

Next you need to remove the relay, two T10 screws, and the wire plug which has two black wires on it.

View attachment 10687

View attachment 10688 This image has been resized. Click this bar to view the full image.
View attachment 10689

Now you need to carefully used a small flat head work your way around the piece being careful not to break any plastic.

View attachment 10722

Once this is done your switch is exposed and you should be able to see your problem.

View attachment 10723

View attachment 10724

A closer look will show you this.

View attachment 10725


Under the cover you can see what all is happening and why your fog lights will not say off. The white plastic piece has worn down and can no longer lift the metal piece far enough to stop the circuit.

View attachment 10726

If this seems to be your problem then your fix will be easy. Next you need to remove one more T10 screw. This will now lift out easily but before you do this remove all the pieces on top that are not secured down.

View attachment 10727

Now you will see the the lifter completely exposed. Pull it up and lightly press it down so you can remove it. I had to slide mine to the left.

View attachment 10728

Now you are ready to put some JB Weld on the part to build it up to its original length. (I used JB quick Weld but either will work) Before this step you might want to clean the part to ensure the glue will stick. I used side cuts to clean the part up from where it had actually smashed/melted down.

View attachment 10729

After the glue has dried you can now put it all back together and test it out.

Thanks so much for this info! Successfully made this fix over the weekend using JB Weld UV SuperWeld….just a couple drops did the trick (held upside down while curing)
 
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I found this thread in a search hoping to find an aftermarket MFS that people had luck with, because wouldn't you know it, it's discontinued from Mopar. 🙄

Should be an easy fix. Such a random issue though. It started flickering on me driving around today and by the time I got home I couldn't get them to turn off without pulling the relay.
 
I’ll chime in, as the fog lights were disconnected on my wife’s TJ when she bought it (it predates me).
She said it was because they always stayed on. Same issue you’re having.

I decided not to replace or fix the MFS. Instead, I pulled the wiring out of the harness, extended them so they would reach the center console, where I added an aftermarket switch that matches the OEM look.

It will never fail like the tiny plastic parts of that shitty design the factory came up with.
 
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I’ll chime in, as the fog lights were disconnected on my wife’s TJ when she bought it (it predates me).
She said it was because they always stayed on. Same issue you’re having.

I decided not to replace or fix the MFS. Instead, I pulled the wiring out of the harness, extended them so they would reach the center console, where I added an aftermarket switch that matches the OEM look.

It will never fail like the tiny plastic parts of that shitty design the factory came up with.

That's not a bad idea. I was holding the last open spot for a front selectable locker but I don't know when or if I'll ever do that. Plus, I still have hard top washer and wiper switches doing no good since I don't even own a hard top.

Early TJs like my 99 had the fog light switch down there anyway, so there would be used factory switches available too.
 
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Finally got time to try this. I used heat shrink & a piece of zip tie to build up the piece. It took me two attempts to get everything back together correctly & working properly. No more fog lights coming on with right blinker & hopefully no more random dead battery. (1/4" diameter heat shrink in case you were curious. )
20230722_084559.jpg
 
Just put my MFS back in and tested it out, works like a charm! Used the JB weld method to fill it in.

The dumbass that made our brake pads sit directly on the knuckles to wear divots into them back in 1990 must have moved over to electrical before the late model TJs MFS was designed. 🙄
 
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