Fog lights not working, calling all electricians Options

[malcolm2]

OK, I know enough about elec. to test a few things so here is what I found once home from Okteenerfest.

Fog lights, driving lights, whatever you want to call them just quit working.

The pull knob lights up
I get 12v in the front trunk at the connection from the main harness. (that is with the connection separated) {with all wire connected, I get no reading}
Grounds have continuity there too.

I did not get 12 volts once I took the light apart, not the bulb holder, just the light was apart and I used an alligator clip to ground it. No volts.

If I remove the alligator clip from the hanging light in the picture below and put the red lead of the VM on the white/ylw wire at the bulb holder THEN the black lead of the VM to a bolt on the car..... I get 12 volts.

So with the bulb holder or the complete fixture assembled and grounded I get nothing.

What is going wrong here?

[messix]

is there continuity on the ground of the socket [outer part the bulb fits into] to the ground on the car?

so if you have the light dismounted from the car and you run leads from light mount to car for you get 12V?

if no, check for continuity from socket to mount of light with ohm function on meter [it should read just like if you touch the meter leads together] ?

if no continuity look for why. broken wire? corrosion?

[messix]

is this a sealed beam light?

[Tom]

Sounds like you have a bad/dirty connection that is losing continuity when a load is applied. The meter reads at the socket because the meter is not applying a load, well yes a load but very small. The bulb has a larger load, so the connection breaks down and you get no voltage reading. Check up stream for all connections, ensure they are clean and tight.
Tom

[Mike Bellis]

If you read 12V on the ground lead, through the lamp, with it disconnected from the car, the circuit is good. You may have a really bad ground. Run a ground lead all the way to the battery negative for testing and see if the lamp will light up.

[malcolm2]

is there continuity on the ground of the socket [outer part the bulb fits into] to the ground on the car?

Can only check that when disassembled. The brass spring touches the bulb holder that touches the outer portion of the bulb. Ground runs thru the metal to the brown wire. I have verified continuity from the outer part of the bulb thru this system to a bolt on the car.

so if you have the light dismounted from the car and you run leads from light mount to car for you get 12V?

NO that is the problem, plus it is both lights not working.

You would think that if you put 12v on the center of the bulb and grounded the outside case of the bulb, the bulb would light up. When I ground it the 12v goes away.

[malcolm2]

If you read 12V on the ground lead, through the lamp, with it disconnected from the car, the circuit is good. You may have a really bad ground. Run a ground lead all the way to the battery negative for testing and see if the lamp will light up.

I will give that a try now.

BTW this is a 75 with back dated bumpers. I added the fogs last year. The harness in the car had covered connections for this.

Both lights are not working and the bulb I have taken apart has continuity.

Going to find a long wire.

[malcolm2]

If you read 12V on the ground lead, through the lamp, with it disconnected from the car, the circuit is good. You may have a really bad ground. Run a ground lead all the way to the battery negative for testing and see if the lamp will light up.

OK, the blue wire hanging down is straight from the battery - side. With the black clip on the horn, and the red one on the bulb center, I get 12v. Car is idling and headlights are on LOW, along with the fog knob being pulled out. Then...



with the black clip on the blue from -BATT I get 0.




edit: not a symptom anymore
Strangely enough, I do NOT get continuity between the blue wire directly from - BATT to a bolt on the car or the horn... (IMG:style_emoticons/default/confused24.gif)

[Dave_Darling]

Strangely enough, I do NOT get continuity between the blue wire directly from - BATT to a bolt on the car or the horn... (IMG:style_emoticons/default/confused24.gif)

I'd say that is a pretty big red flag there. Time to start checking all of your grounds. Remember that paint is not a good conductor, so if you're checking on painted parts you may need to wire-brush the paint away.

--DD

[malcolm2]

OK, must have been something in my rig from the batt - to the front of the car. I now get continuity between the blue test wire from batt- and any metal I touch.

Just to be sure I took two test leads at the battery and made the bulb come ON. I was getting continuity, but wanted to see it work.

I have checked around the car and don't see any obvious ground issues. I check continuity with the blue wire all over the car.

So I still show 12v at the bulb when the ground to the bulb is not attached, and 0 when it is.

[Mike Bellis]

If you have 12V to the light, the problem is with the light or a connection, most likely ground. In fact, try a new lamp. On very rare occasions, they can be bad, have continuity and not light up.

[malcolm2]

If you have 12V to the light, the problem is with the light or a connection, most likely ground. In fact, try a new lamp. On very rare occasions, they can be bad, have continuity and not light up.

It lit up with test wires directly to the correct places on the bulb. Both lights, right and left are out.

I have pulled my elec. drawing from Prospero's garage and it does not have driving/fog lights on it. I see no white/yellow wires on this whole drawing.

[76-914]

Look at the bulb carefully to see if the tungsten filament is broke and sometimes making contact. If you tap it slightly you will see if it separates.

[76-914]

Look at the bulb carefully to see if the tungsten filament is broke and sometimes making contact. If you tap it slightly you will see if it separates.

[messix]

check and clean contacts on fuse 10

[malcolm2]

Look at the bulb carefully to see if the tungsten filament is broke and sometimes making contact. If you tap it slightly you will see if it separates.

I get continuity and I lit it up. Plus both lights are out and went out at the same time. I was hoping to find someone that has the same problem or that could follow my description of the symptoms.

I too feel that it could be related to ground. But, if I place the VM on continuity and one lead on the connector on the brown wire or the flat brass spring, both attached to the fixture and the other VM lead on a non-painted screw and get continuity, wouldn't that rule out that ground wire?

If the + wire( wh/ylw) was touching metal, wouldn't the other stuff in the car being going crazy?
And might I get continuity between the + lamp connection and ground or other non painted metal?

[messix]

do you have amp draw feature on you vom?

if you do set the leads in the proper config, disconnect the hot lead for the light, then connect the leads to the hot wire from the car and then the other to the hot lead of the light and observe to amp load, if there is no load check it at the splice in the trunk, still no load check fuse 10 on the fuse panel.

there is a relay behind the fuse panel and that might be faulty also where it will not supply a loaded circuit.

[malcolm2]

do you have amp draw feature on you vom?

if you do set the leads in the proper config, disconnect the hot lead for the light, then connect the leads to the hot wire from the car and then the other to the hot lead of the light and observe to amp load, if there is no load check it at the splice in the trunk, still no load check fuse 10 on the fuse panel.

there is a relay behind the fuse panel and that might be faulty also where it will not supply a loaded circuit.

I don't have AMP draw feature, but I can grab an AMP meter from my guys at work and check it out tomorrow.

You mentioned the relay, and it made me think. I have not upgraded the wiring so the fogs operate only when the headlights are LOW beam. The fogs shut off when you switch to HIGH beam. The relay is probably what does that, so it is acting like the beams are on high.

Driving to Okteenerfest on Saturday morning, it was dark enough for headlights and my HIGH indicator on the dash is not very bright. I think I had my high beams on all morning.

I will search to find which relay and if it is one of the standard ones, I have some spares.

BTW: fuse 10 is clean and tight.... another thing I did with this car is that I have upgraded the fuse box, so it is brand new, 6200 miles.

[malcolm2]

J5 Is the one. Bowlsby had it.

[malcolm2]

(IMG:style_emoticons/default/icon_bump.gif) for more conversation and some results.

I have 2 spare relays. I tested them per the picture below: WHile checking continuity between 30 and 87 you put a 12volt power source on either 86 or 85, then you ground or put a batt- on the other. When you touch the relay with the last wire, listen for the relay to click and watch your meter for continuity.

my spare relays and the one I just took out of the fog light spot on the panel under the dash are operating.

So I took a flashlight under and found that 87 could not be doing it's job.

So what would make this melt? Yes heat, but how did it get hot.

I don't want to just get a new relay seat, or rewire and have this happen again.