Factory fogs question

So newish to the XJs for stuff like this and im HORRIBLE at wiring stuff. SO girlfriends 97 is a fully loaded country. came with factory fogs they were all hazy and seen there time. i replaced them with new factory style replacement ones. they worked perfect for about a month then it snowed the first time then they didnt work any more. so next nice day i went to inspect why. glass is good plugs good bulbs good. checked the switch and it was good still and tried a junk yard one to see hey why not which was also good. her xj also has a weird wiring kit with a relay plugged into it with a mopar number on it and i have never seen on any other XJ i have ripped apart in a junkyard with one. but all that looked good. checked the fuse in the fuse box in the engine bay it was blown thought cool just a old fuse blew. replaced it put the switch on only one worked then the fuse popped again. any ideas?

Like most other XJ Cherokee issues, you need to test and inspect to find the root cause.

Grab your $6-18 volts/ohms multi-meter you bought at the local hardware store, auto parts store, or WalMart type store and test for wire continuity, short circuits, good grounds, and 12 volts. Inspect the wire plugs and wire harness for damage and corrosion, and/or chafed wire insulation. Start testing at the lamps, and work your way back to the relay, and on back to the switch. Don't forget to check all the fuses in both fuse boxes, and to apply 12 volts directly to the lamps.

anyone know where the ground is located for them its hard to trace the wires

Few thoughts.

The lamps worked before you changed them.
-were the replacement lamps OEM type with factory connectors or did you have to splice them in?
-check your wiring job for stray strands of bare wire, chaffing.
-check that you wired them correctly
-the fact that only one worked tells me the wiring is not happy past the PDC. They are wired in parallel, so unless a bulb went, there is something not correct.
-what is the lamp rating of your new bulbs. I believe the factory lamps were 55w or less (cant find spec).

The fuse blew
- the fuse is a 10A for the fog lamp relay coil not the fog lamp current path. The relay supplies a path from fused battery power to the fog lamp circuit. It is a when and how type ( if the headlamps are on, high beams are not). If you are blowing a fuse, the relay itself may be bad.

according to a schematic, the fog lamp circuit is kinda funky, most control circuits have high current power (well 8.5A in this case), sitting on one side of a relay. The control switch usually is in the relay coil circuit (in the milliamp range). So when you flip a switch, the relay coil engages, contacts close bringing higher current from the battery(fused) to your device.

In the Jeep, the relay is controlled by the headlights and high beams for on and off. Once you turn on your headlights, power comes from the battery (fused), back into the cabin and sits at the fog lamp switch. You flip the switch and it goes to the fog lamp harness.

So if you used higher watt lamps you could have toasted your wiring.


From here I would:
-change the relay, if that does not work
-wire the fogs externally

One last note, you said there was another mopar relay in the harness, trace the wiring back, does it splice back in the factory harness or is it straight to the PDC?

they are factory replacements the under the bumper factory installed plug and play ones. not aftermarket hella or kc or anything fancy. the the relay is plugged into the factory harness with a female connector and a male one into the switch with a relay in the middle. next time i have her jeep il take a picture maybe it will be more helpful

Another option, is to fashion an external harness.

First, replace your fog lamp relay in the pdc. The issue may only be the relay.

You will need
-14 or 12 guage wire
-one weatherproof fuse holder and 10-15A fuse)
- Automotive relay and holder
- eyelet butt connector
-tie wraps for dressing and wire loom to prevent chaffing


- disconnect the fog lamps
-wire the fog lamps in parallel, one lead to chassis ground(a damn good ground with paint scraped off and tight) the other lead to pin 87 of your relay
-run a 14g wire (for 55w) or 12g for 100w. Eye connector from the 12v bus (the lug at the front of your pdc), to a fuse (10A-15A for 55W) , then to pin 30 of your relay.
-run a ground to wire from pin 85 of the relay to chassis ground
- run a wire from pin 86 of the relay and splice it to the old positive lead from your fog lamp connector. whichever is closest.


Here is my thinking for this circuit: you already have factory wiring, and seems that it can no longer handle the higher current of the fog lamps, but it should be able to handle the few milli-amps of an aftermarket automotive relay.

instead of actually powering the fog lamps, your existing fog circuit will power the relay, which in turn will take power from your DC bus to your new fog lights.

As long as you dress your wiring correctly and fuse it with a weatherproof fuse holder, you should be good.

Jeeps are notorious for crappy headlamp and fog wiring, over time you will notice dim lights and other issues.
You can apply the same principle for your headlamps with a new external H3 or H4 wiring harness (around $20 on ebay http://www.ebay.com/itm/APC-Univers...Parts_Accessories&hash=item56715f53ed&vxp=mtr). It uses the old headlamp current path to control the relays in the new harness. This way you do not have to mess with wiring through the firewall etc. The linked eBay is for headlights, I have not seen one for factory fogs.

I already have Crowns h4 conversions in there. love them night and day difference. But when I get the XJ back im going to chase the wires and see if is just something dumb like corrosion or something. its been so cold i havent had the effort to do anything il check it out and get back to you guys thanks for the info

I would check the fog light switch, I thought it was a common problem for them to get too hot for the reasons stated above and melt. When I had issues years ago I found the switch was melted inside.

That relay is a TSB fix for the melting switches.



Like was said before. If one is not working, and the fuse keeps blowing I look for a short starting on that side.

^ YES i have never seen it before. tomorrow im dropping her off at the train and taking the XJ im going to try and diagnose it and il get back to you guys. i know the switch is good the little light even works and i have taken it apart and inspected it.