Fog light install worked then didn't

t00th

t00th

TJ Enthusiast
Joined
Apr 26, 2019
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Location
SE PA
Hey all. I know this topic has been covered and I've searched but can't quite find my specific issue.

No pigtails for foglights from factory.

Hella 500 fogs, installed on front bumper, wired up with the less-than-great included wiring harness. These lights have one wire to power, and one short wire to ground--grounded both to the body near where they come out under the wheel wells.

I tested with all the wiring still in the engine bay while waiting for a better switch to arrive--and they worked. Just temporarily grounded the 3-prong switch to metal in the bay

But once I ran the wiring into the cabin through the big rubber grommet on the driver's side and hooked everything up, they're not working--either with the crappy HELLA-supplied switch or the new one I got. I installed the switch on the steering wheel cowl opposite the headlight plunger switch, and grounded to what I THINK may have been aluminum so perhaps that's why the lights won't turn on now? Maybe I just need a better ground? Or is the ground just so that the LED in the switch works?

I have a multimeter but will admit I'm an electrical/wiring absolute newbie, so I don't even know how to use it or where to start checking for continuity to find the source of my problem.

Just weird that nothing has really changed other than the wires being inside the cabin now versus in the engine bay, which is why I think maybe it's a bad ground at the switch.

help welcome!
 
Use the multi meter. This is DC and in the 12 volt range, so make sure the multi meter is set to DC and to the right range. Test it on the battery terminals to see if it reads 12 ish volts. If you probe the battery backwards, it will read -12 ish volts.

Then start probing stuff. Turn all your switches on, and your car on, (and maybe the lights?) and probe the two contacts in the wire harness that connects to the lights. Should read 12 (or -12 if you probed them backwards) . If it does not read anything you can check your ground, by placing one probe on the positive contact on the wire harness at the light, and the negative probe on some bare metal, or the engine. If that then reads 12, then you have a bad ground. If if you get nothing in either situation, then you need to probe the switch. If you get nothing at the switch, then you source for power isn't working.
 
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A couple of things: aluminum is a very good conductor so that is not the problem. And the ground to the switch is most likely only needed to make the light in the switch turn on. Make sure you have the switch wired right. Of the three leads, one is incoming, one is outgoing and those two can be swapped no problem. The ground only needs to be grounded if you want the switch to light.
 
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If it worked and then didn't, check the fuse in your wiring. I'm sure that light bar came with a fuse. If not, then just follow the previous advices.
 
If the lights are grounded, then your switch needs power. You should not have had to ground the switch to make the fog lights come on. You could have easily blown a fuse trying to do that. Also, if the switch light is LED, it needs to be wired a certain way to work properly.

Additionally, you really should use a relay (under the hood), to control the power to the lights. Less amps through the switch inside the cab.
 
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So-- couple things. The harness does in fact include a relay and a fuse. It's a three-prong LED switch, so it sounds like the ground is just for the LED to come on so my issue is not a ground at the switch.


The thing is, they absolutely worked when I first installed them. So it's all wired up correctly. It seems like my issue is that I lost a connection or a ground somewhere when I was yanking on everything to get it through the firewall grommet.

I'll start multimetering around, this has all been very helpful, thanks to everyone who responded.
 
I'm a wiring newbie. I blew a fuse. Don't know why it didn't occur to my dumb ass to look there first. Just didn't think I had done anything that could've blown it, since I didn't really do much besides run the wiring through the firewall.

They work great.

Thanks to everyone who chimed in. I'm learning. Slowly but surely.
 
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t00th said:
I'm a wiring newbie. I blew a fuse. Don't know why it didn't occur to my dumb ass to look there first. Just didn't think I had done anything that could've blown it, since I didn't really do much besides run the wiring through the firewall.

They work great.

Thanks to everyone who chimed in. I'm learning. Slowly but surely.
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Glad you found your problem. That's the way I've learned some of my lessons. I had a high suspicion it was that fuse. 👍
 
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