Hey guys, the factory fog lights on my 2001 Cherokee do not work. Here's what I've figured out so far:

1: When the key in the on position, headlights on, the light in the fog light switch comes on when it is switched on.
2: fog light relay 1 and 2 work. I bench tested them for function, control side continuity, and NO/NC settings. No resistance on the load side when relay pulls in. I also pulled each in and out of the PDC and felt/heard them clicking when the fog light switch is in the on position.
3: checked for voltage at the connectors at the bumper. No voltage present when switch is activated.
4: Checked for voltage at fog light relay socket when switch is on. There is voltage there. When I tried to jumper the load side connections, the light still refused to come on.
5: Verified ground from fog lamp negative to negative terminal on battery with no measurable resistance.

What I do know:
1: When the headlights are on, the green light in the fog lamp switch comes on when the switch is turned on.
2: When high beams are turned on, the green light in the fog lamp switch turns off, which tells me that the two relays appear to be functioning properly (I remember back in the day, I wired in some daytime running lights in my old truck with a high beam bypass relay that did the same thing).
3: After pulling the back cover off the PDC, I could see no indication that the wires coming from each relay socket were burned up, damaged, or otherwise destroyed.

After looking for a key to identify some of the fuses in the PDC, my factory service manual came up a bit short. It only showed me numbers and codes, but didn't identify if any of the small fuses in there were between the relays and the fog lights. I know that fuse #7 in the in-cab fuse block is working because a bunch of other crap wouldn't work without it.

Any thoughts?

Thanks so much in advance!

 

Edit.. previous post based on 96 FSM, not correct for your year. Previous years ran the power to the driving lights through both relays, then through the switch, then off to the lights. Switch failures were common.
Yours has a "fix" for that, using the switch to control relay #2. Drawing below.
Relay #1 operates if the parking lights are ON and the high beams are OFF, and supplies 12 volts to the dashboard switch. Operating the switch activates relay #2, which provides power to the lights.
Lamp power is through one of the small PDC fuses, #25 (15amp). Bottom-left fuse position, assuming the gen/bat terminals are at the bottom.

 

Thanks for the help Radi. I will check that fuse out when I get home from work. I also noticed that the wiring diagram in my FSM indicates a connector near the electric cooling fan that I missed (I assumed incorrectly that it was simply spliced into the harness prior to going to the bumper). So now I have two more things to check when I get home.

 

It seems you were right. I checked that fuse in the PDC and sure enough, it was blown. It wasn't like the rest, so I know it's been replaced before. Guess I'm just going to run it and see if it becomes a problem and go from there.

Again, than you for the assist. It's appreciated.

 

Well if you keep blowing the fuse you must have a short somewhere in the that system.

 

It's possible. The fog lights aren't factory. They are some cheap aftermarket knockoffs that the previous owner spliced into the original harness that connects to the factory wiring behind the bumper. I'm just glad they didn't cut away the factory connectors and splice them in themselves. I'm going to get some OEM lights and new harnesses to connect to the factory connectors.

 

15 amps (fuse rating) X 13.5 volts = 202 watts. What is the total wattage of your lamps?

 

Don't know. They are cheapo knock off lights. I'm going to buy factory ones and put them back because I know the fuse can handle them, provided there isn't a short in the system somewhere. It's either that or some Hella 55watt fog lights, which will be 110 total watts; well within the amp rating.

 

The factory fogs are wired into the low beams circuit. When you switch to high, they go off.

 

There are a few different configurations, but most appear use some method of grounding a control line through the high beam lamp on the driver's side. When the high beam turns on, the "ground" has 12V on it and kicks the relay out. Did they change that at some point to use the low beam circuits?

 

FSM Claims that power is fed from the left headlamp.