Fog light wiring

[pfran42]

I noticed my passenger-side fog light was out so I took a look at the bulb which looked OK, reconnected it and re-tested. Still no pass side fog light. All the fuses checked out OK so I went to Autozone and purchased another lamp just in case I missed something on the one that was installed on my Cruiser.

Still nothing...

I have a sound electrical system that has never behaved strangely.

The wiring trunks into a thicker wrapped bundle shortly after leaving the fog lamp and I don't want to start tearing it apart chasing down a short (wouldn't that blow a fuse anyways?) before checking here to see if I am missing a troubleshooting step...

Any ideas?

 

[dclee]

I noticed my passenger-side fog light was out so I took a look at the bulb which looked OK, reconnected it and re-tested. Still no pass side fog light. All the fuses checked out OK so I went to Autozone and purchased another lamp just in case I missed something on the one that was installed on my Cruiser.

Still nothing...

I have a sound electrical system that has never behaved strangely.

The wiring trunks into a thicker wrapped bundle shortly after leaving the fog lamp and I don't want to start tearing it apart chasing down a short (wouldn't that blow a fuse anyways?) before checking here to see if I am missing a troubleshooting step...

Any ideas?

Did you test continuity at the plug with a multimeter?

 

[r2m]

You need to get a multi-meter. That'll help you chase down a short.
First, it could not be a fuse. A fuse is for an entire circuit, not just one light.
Second, when you get a multi-meter (Radio Shack for about 20 or 30 clams), you should be able to chase it down pretty easy.
You would not normally get a short in the loom, because of it being protected by the rest of the wrap. It can’t bend or twist as an individual wire. And if there should be a broken wire in the loom, it would not short anything out because everything around it is insulated and then wrapped. So my guess is that the short would be from the light to where your wires start coming together. It could be a loose connection at the light too. If you can, try to jiggle around the area with the lights on and see if anything happens.

All this coming from a Mechanical Engineer……
But just follow common sense.

 

[pfran42]

You need to get a multi-meter. That'll help you chase down a short.
First, it could not be a fuse. A fuse is for an entire circuit, not just one light.
Second, when you get a multi-meter (Radio Shack for about 20 or 30 clams), you should be able to chase it down pretty easy.
You would not normally get a short in the loom, because of it being protected by the rest of the wrap. It can’t bend or twist as an individual wire. And if there should be a broken wire in the loom, it would not short anything out because everything around it is insulated and then wrapped. So my guess is that the short would be from the light to where your wires start coming together. It could be a loose connection at the light too. If you can, try to jiggle around the area with the lights on and see if anything happens.

All this coming from a Mechanical Engineer……
But just follow common sense.

Thanks for the advice. I have a multimeter. I'll test it out and report back this evening.

 

[nomembername]

First things first, check the ground.

 

[1loudLX]

It's covered in snow/ice here, how about there?



Could the replacement bulb be defective?

 

[pfran42]

It's covered in snow/ice here, how about there?



Could the replacement bulb be defective?

Low 40s and overcast....I don't think so. You can clearly see the entire filament on the old and new bulbs.

 

[nomembername]

It's covered in snow/ice here, how about there?
Could the replacement bulb be defective?

About the same.

Any bulb could be defective, but to have two that look fine and are defective? Those are slim odds.

Rust is not a very good conductor, chances are that's the problem more than wires or bulbs. Especially since the OP says he tested not just with a new bulb but a new lamp. Did the new lamp get a new ground, or was it tested using the existing hookup? If the ground is bad, no test lamps or replacement bulbs will work.

 

[pfran42]

About the same.

Any bulb could be defective, but to have two that look fine and are defective? Those are slim odds.

Rust is not a very good conductor, chances are that's the problem more than wires or bulbs. Especially since the OP says he tested not just with a new bulb but a new lamp. Did the new lamp get a new ground, or was it tested using the existing hookup? If the ground is bad, no test lamps or replacement bulbs will work.

I misspoke. I purchased an additional BULB. Sorry. So I should check for a ground connection on the lamp housing itself?

 

[EdsCruisin]

I misspoke. I purchased an additional BULB. Sorry. So I should check for a ground connection on the lamp housing itself?

The lamp housing is not grounded. It is sitting in a big rubbermaid bumper. There are only two wires to each lamp - positive and neutral and they are direct to the bulb. They don't even touch the lamp housing.

You need to test the continuity at the plug socket. Test both positive to frame ground and positive to neutral. Other than bad bulbs, you probably have an open circuit. Bad bulbs happen. The last few of mine that have blown, have not shown any outward signs of being bad at all.

 

[LCHardriver_02]

Agreed. Check for the 12V and then check for continuity to ground through the socket. This will tell you if you have an open on the power side or ground.

 

[nomembername]

I misspoke. I purchased an additional BULB. Sorry. So I should check for a ground connection on the lamp housing itself?

If it's metal, it may be self-grounding. If it's plastic, it should have a ground wire, either off the pigtail to the socket leading to a short ground wire (which might attach, say, onto the bumper horn) or into the harness (which should split out to a ground lead somewhere around the radiator support typically). I'd expect it would go into the harness and chase back to a chassis ground. If the ground wire is good, then the next check is for power to the other side of the fog light lead. If yes, then test continuity through the fog lamp socket. If no, then you have a problem in the wire harness which needs to be traced.

You can rule out the switch, the fuse, and the junction box relay if one side is lighting up.

These are generally the first steps for any electrical troubleshooting - are you actually making a circuit.

 

[nomembername]

The lamp housing is not grounded. It is sitting in a big rubbermaid bumper. There are only two wires to each lamp - positive and neutral and they are direct to the bulb. They don't even touch the lamp housing.

You need to test the continuity at the plug socket. Test both positive to frame ground and positive to neutral. Other than bad bulbs, you probably have an open circuit. Bad bulbs happen. The last few of mine that have blown, have not shown any outward signs of being bad at all.

When did a DC circuit gain a neutral leg?

 

[pfran42]

If it's metal, it may be self-grounding. If it's plastic, it should have a ground wire, either off the pigtail to the socket leading to a short ground wire (which might attach, say, onto the bumper horn) or into the harness (which should split out to a ground lead somewhere around the radiator support typically). I'd expect it would go into the harness and chase back to a chassis ground. If the ground wire is good, then the next check is for power to the other side of the fog light lead. If yes, then test continuity through the fog lamp socket. If no, then you have a problem in the wire harness which needs to be traced.

You can rule out the switch, the fuse, and the junction box relay if one side is lighting up.

These are generally the first steps for any electrical troubleshooting - are you actually making a circuit.

Well, since the other fog light comes on when I turn them on, I don't think it is the switch. Now if I can just find my Multi-Meter...

 

[nomembername]

Well, since the other fog light comes on when I turn them on, I don't think it is the switch. Now if I can just find my Multi-Meter...

So we agree... "You can rule out the switch, the fuse, and the junction box relay if one side is lighting up. "


A test light is a simple enough continuity tester... if it's a circuit, the bulb lights up.

Oh yeah, check that bulb too!

 

[pfran42]

So we agree... "You can rule out the switch, the fuse, and the junction box relay if one side is lighting up. "


A test light is a simple enough continuity tester... if it's a circuit, the bulb lights up.

Oh yeah, check that bulb too!

Isn't the "test light" the issue to begin with? I mean I have tried two bulbs and nothing. I couldn't find my multi-meter last night. I am going to stop by AutoZone today and see if they will let me borrow one.

 

[nomembername]

Isn't the "test light" the issue to begin with? I mean I have tried two bulbs and nothing. I couldn't find my multi-meter last night. I am going to stop by AutoZone today and see if they will let me borrow one.

No. This is a test light:

 

[EdsCruisin]

When did a DC circuit gain a neutral leg?

Correct, but I was trying to differentiate the ground wire in the circuit from a new frame ground.

Having worked with these wires - there is no metal in the fog lamp and the circuit is all in the wires, which trace up to the loom behind the headlamps. There are several grounded wires along each fender, just below the hood line. It likely ties to one of those, but not near the bumper anywhere.

 

[pfran42]

I am a Dumb@55...I purchased the light tester and everything was fine from the circuit side. I looked at the lamp-side connector fitting and the channel that the bulb slides into was encrusted in dirt. I used the test light probe to clean it and I have a working passenger fog light!

One other thing. The lamp lens was all fogged up and had water droplets all over it. I noticed what appears to be a vent near the top of the lap housing (when looking at it from the rear). It is gray, comes directly out (horizontally) and then makes a 90 degree turn so that the "vent" opening is facing towards the road. Is this designed to not be 100% waterproof and to let the heat from the bulb dry out the condensation and vent it outside the lamp housing?

I plan on replacing the o-ring on the lamp housing and using an electrically safe grease on it to keep out moisture. The 10 minute drive back from the parts store dried out the lamp housing but I was just wondering if the a little moisture is allowed in there in the first place (with the "vent" and all).

 

[r2m]

I am a Dumb@55...I purchased the light tester and everything was fine from the circuit side. I looked at the lamp-side connector fitting and the channel that the bulb slides into was encrusted in dirt. I used the test light probe to clean it and I have a working passenger fog light!

One other thing. The lamp lens was all fogged up and had water droplets all over it. I noticed what appears to be a vent near the top of the lap housing (when looking at it from the rear). It is gray, comes directly out (horizontally) and then makes a 90 degree turn so that the "vent" opening is facing towards the road. Is this designed to not be 100% waterproof and to let the heat from the bulb dry out the condensation and vent it outside the lamp housing?

I plan on replacing the o-ring on the lamp housing and using an electrically safe grease on it to keep out moisture. The 10 minute drive back from the parts store dried out the lamp housing but I was just wondering if the a little moisture is allowed in there in the first place (with the "vent" and all).

Gotta love simple fixes!! Just wish they all were that simple.