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check factory fog light wiring

4x4JeePmaNthINg

NAXJA Forum User
Location
Colorado
hey all, when i bought my jeep the factory fogs were toast and have since been removed. I know this might be a dumb question but do i test the leads on the remaining wires for 12v to make sure they are still getting power? im thinking of just buying the same factory style cheap fogs but i want to know it was just the lights that were bad before.

also do the headlights need to be on/off/ hibeam anything speacial to normally run these i never knew how they worked.

if not what am i looking for with a multimeter, im clearly in the dark here

thanks for the help
 
My factory fogs work with the Jeep ignition off, but headlights on - I find that odd but it's how it's always been. Either way, have the headlights on low beam, stock switch on, and test the factory connectors for 12v power with a test light. That will tell you if you getting any power. If not, move up the line, checking the wiring, and then the relay in the PDC, then the fuses, etc. The factory fogs turn off with the high beams. The factory fogs are actually quite useful (properly taken care of) and put out a good beam spread (I added a harness for cleaner power).
 
ok i bought a test light. i cant seem to find a 99 xj pdc diagram that tells me what Fuses are for what, just the relays.

I turned on the head lights and grounded the test light to the battery. I checked the fog plugs with no luck, then i checked all the pdc fuses. There were two that did not light up. I replaced them and still they did not light up so i pulled the dash off and removed the fog switch. I am getting power to the switch, maybe its a bad switch. with the switch out i went back and tested the two fuses that didnt light up and the tester lights up with the switch removed.

Does this indicate a bad switch or possibly relay?
 
These switches can be a problem 'cos they over heat.

Probably the simplest test is to see if the green warning light comes on, idf it does but still nothing at the connectors, it's a wiring issue.

Next just bypass the switch. It can be overhauled, easily & successfully: there's a "how to" post on here somewhere.

PartsMonster is a good source of reasonably priced replacements - if it really comes to that.
 
Do you have a multimeter? To test the switch you just measure the resistance of the switch, when it's off it should be high resistance (megaohms) and when it's on it should be low resistance (milliohms). Also, most multimeters will have a connection tester that will beep if there is a connection (i.e. switch on).

If you don't have a multimeter, you can use the test light. If one terminal of switch is connected to 12V, the test light should turn on when touched to the other terminal of the switch.
 
Fog lights are only supposed to work with the low beams on. I'd test for voltage that way. Look for a fuse first.

Low beams or parking lights. There is relay logic that keeps them off when the high beams are on.

Side note: if you are running a relay harness (or possibly LEDs), you need to put a relay in behind the driver's side headlight to un-ground the fog light relay coil when the high beams are on. That wire relies on the driver's side high beam filament to ground the fog light relay coil (that's how the fogs go off when you hit the brights) and if you're running a relay harness that may result in the high beams sticking on - it did for me.

If you're running LEDs it may cause the high beams to glow if the fogs are on.

Also, obviously, if your DS high beam is burned out fogs may not work. Not sure if it will then ground through the pass side high beam filament or not. Definitely fogs will not work if both high beams are burned out or if you don't have headlamps installed.

There are two relays related to the fog lights; if someone removed the factory fogs they may have removed those relays as well.
 
Do you have a multimeter? To test the switch you just measure the resistance of the switch, when it's off it should be high resistance (megaohms) and when it's on it should be low resistance (milliohms). Also, most multimeters will have a connection tester that will beep if there is a connection (i.e. switch on).

If you don't have a multimeter, you can use the test light. If one terminal of switch is connected to 12V, the test light should turn on when touched to the other terminal of the switch.

maybe a dumb question but can this still be done for power off if i unplug the switch?
 
Yes, but if it is disconnected you will need to connect one end of the switch to a 12v source with an alligator clip or something to use the voltmeter. The light should turn on if the switch is on, the light should be off if the switch is off. Using a multimeter the switch can be disconnected see an example here on Youtube: https://www.youtube.com/watch?v=lB-aULIjiog
 
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Just my opinion-


Fog/driving/light bar...........should be wired independently with it's own harness just as with the headlight harness.

My bar is activated by the brights switch and I have an on/off switch on the dash........this is all done with relays.

Never have full current load through a dash switch........relay trigger only, neg preferred.
 
Just my opinion-


Fog/driving/light bar...........should be wired independently with it's own harness just as with the headlight harness.

My bar is activated by the brights switch and I have an on/off switch on the dash........this is all done with relays.

Never have full current load through a dash switch........relay trigger only, neg preferred.
agreed but i would like to use the factory switch. If i can wire this to run aux lights independently from the headlights im better off. I have a headlight harness (pulled factory fog relay for hi/low switchability) and will most likely have to add a new harness, but if i can also keep the stock mounted switch it sure would be nice.
 
Yes, but if it is disconnected you will need to connect one end of the switch to a 12v source with an alligator clip or something to use the voltmeter. The light should turn on if the switch is on, the light should be off if the switch is off. Using a multimeter the switch can be disconnected see an example here on Youtube: https://www.youtube.com/watch?v=lB-aULIjiog

switch is out, does it matter which end is clipped to 12v?
 
i think it does if its a 3 wire. because of the light on the switch. id have to guess that if you had them swapped the indicator light would be stuck on.
 
Found this on another forum:

145225d1441756656-xj-oem-fog-light-wiring-front-lighting_page_7.jpg


http://www.cherokeetalk.com/forum/f8/xj-oem-fog-light-wiring-57745/

You can see how the switch is wired. When the switch is on connections between 3 and 2 should be shorted. So if you apply 12V to either 3 or 2, and turn the switch on, the voltage tester should detect voltage at the other terminal. It doesn't matter which one you apply 12v to, you should just detect voltage on the other one when the switch is closed.

Normally you'd use a multimeter continuity tester to test this, but this is a kinda roundabout way of testing it using a voltage tester.
 
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