Fog lights don't work
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Teching In
Joined: May 2006
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Fog lights don't work I have a 1998 Trans Am that I have owned since new. I have approx. 34k miles on it. The last 3-4 years I have had increasing trouble getting the fog lights to work. I replaced the switch and that didn't fix the problem. The fog lights will work for the first week or two after I take the car out of storage from the winter and then don't work any more for the rest of the year. Anybody have any ideas on how to fix them?
TECH Enthusiast
Joined: Dec 2005
Posts: 510
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From: NW burbs of Chicago
Sounds like corrosion somewhere in the wiring. Dries out during storage. Then starts up again when its out in the world awhile. Trace both the ground and the hot back a few connections. Clean em and di-electric grease em.
Car sounds like a keeper!
Have you been reading here awhile? Or just found the place? One post!
Car sounds like a keeper!
Have you been reading here awhile? Or just found the place? One post!
Mine has the same problem, 99 T/A mostly stock. Fog lights worked fine and then they both just quit at the same time. I've replaced the relay. I've checked the bulbs and the wiring that i could trace around them and found nothing. The switch inside lights up like normal when you try to turn them on. What else could it be??
I've found this problem in other posts but none of them has a solution!!!
I've found this problem in other posts but none of them has a solution!!!
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Verdad Gallardo
Joined: Nov 2003
Posts: 11,329
Likes: 346
From: Jacksonville, FL (originally from Toronto Canada)
The fog light wiring is very basic so quite easy to test/diagnose with basic equipment and electrical knowledge. The relay is the central device in the circuit so testing starts there. Get a test light or multimeter and check the following:
- Remove the fog light relay from its socket
- Turn on the headlight switch and fog light switch
- Check for power in the relay socket in the E11 (brown) and F11 (yellow) pins. Those are the two pins that are closest to the outside edge of the junction box - E11 is closest to the fan relay and F11 is closest to the fuses. If E11 has no power, check the TAIL LPS fuse, the headlight switch, and the brown wire from the headlight switch to the relay. If F11 has no power, check the fog light switch and the yellow wire from the switch to the relay.
- This is where a test light is actually better than a multimeter. If you have one, connect the clip end to battery power (the battery terminal bolt on the junction box is a good place) then touch the probe tip to terminal F9 (purple) in the relay socket. F9 is the terminal at the other end of the relay socket (next to the horn relay) closest to the fuses. Your fog lights should turn on (along with the test light bulb). If they don't, check the purple wire from the relay to the lamps, the lamp bulbs, and their grounds. If you don't have a test light, you can use a piece of wire but it would be best to use one with an inline fuse to avoid short circuits (the test light bulb provides a small load that prevents a short).
- Take your test light with the clip still attached to the power source and touch the tip to terminal E9 (light green) next to the F9 terminal you just tested. If the high beams are off, the test light should illuminate. Using a fused piece of wire instead will make your high beams illuminate (you're back feeding current to them).
- If all those things check out then the relay is the problem. Try swapping the horn relay into the fog light relay socket and see if the lights work.
Registered User
Joined: Mar 2023
Posts: 2
Likes: 0
Fog light Diagnostic Question The fog light wiring is very basic so quite easy to test/diagnose with basic equipment and electrical knowledge. The relay is the central device in the circuit so testing starts there. Get a test light or multimeter and check the following:
- Remove the fog light relay from its socket
- Turn on the headlight switch and fog light switch
- Check for power in the relay socket in the E11 (brown) and F11 (yellow) pins. Those are the two pins that are closest to the outside edge of the junction box - E11 is closest to the fan relay and F11 is closest to the fuses. If E11 has no power, check the TAIL LPS fuse, the headlight switch, and the brown wire from the headlight switch to the relay. If F11 has no power, check the fog light switch and the yellow wire from the switch to the relay.
- This is where a test light is actually better than a multimeter. If you have one, connect the clip end to battery power (the battery terminal bolt on the junction box is a good place) then touch the probe tip to terminal F9 (purple) in the relay socket. F9 is the terminal at the other end of the relay socket (next to the horn relay) closest to the fuses. Your fog lights should turn on (along with the test light bulb). If they don't, check the purple wire from the relay to the lamps, the lamp bulbs, and their grounds. If you don't have a test light, you can use a piece of wire but it would be best to use one with an inline fuse to avoid short circuits (the test light bulb provides a small load that prevents a short).
- Take your test light with the clip still attached to the power source and touch the tip to terminal E9 (light green) next to the F9 terminal you just tested. If the high beams are off, the test light should illuminate. Using a fused piece of wire instead will make your high beams illuminate (you're back feeding current to them).
- If all those things check out then the relay is the problem. Try swapping the horn relay into the fog light relay socket and see if the lights work.
Joined: Nov 2003
Posts: 11,329
Likes: 346
From: Jacksonville, FL (originally from Toronto Canada)
The light green wire is connected to the power side of the high beams circuit. It's set up that way so that when the high beams are on there's no ground for the fog light relay and the fog lights will be off while the high beams are in use.
Applying power to the light green wire through a test light should illuminate the test light bulb and may or may not also illuminate the high beams depending on how much current can flow through test light to the high beams. It's an electrical impossibility for the test light to pass power to the high beams but not illuminate itself because the power has to flow through the test light bulb to get anywhere. That's assuming a good old fashioned test light rather than one of the fancier new electronic ones.
In any case, if you got to step 5 in the list, just skip it and try swapping the horn relay into the fog light socket and see if the lights work. That whole diagnostic procedure I listed was more about proper diagnostic steps than it was about quickly determining the cause of the problem. In practical terms the list should have been: 1. Swap the horn relay into the fog light relay socket. If it works then the relay was the problem, otherwise start checking wires as described in the original list. It's much more likely that the relay is the problem than the wiring unless you have reason to suspect the wiring might be damaged.
Applying power to the light green wire through a test light should illuminate the test light bulb and may or may not also illuminate the high beams depending on how much current can flow through test light to the high beams. It's an electrical impossibility for the test light to pass power to the high beams but not illuminate itself because the power has to flow through the test light bulb to get anywhere. That's assuming a good old fashioned test light rather than one of the fancier new electronic ones.
In any case, if you got to step 5 in the list, just skip it and try swapping the horn relay into the fog light socket and see if the lights work. That whole diagnostic procedure I listed was more about proper diagnostic steps than it was about quickly determining the cause of the problem. In practical terms the list should have been: 1. Swap the horn relay into the fog light relay socket. If it works then the relay was the problem, otherwise start checking wires as described in the original list. It's much more likely that the relay is the problem than the wiring unless you have reason to suspect the wiring might be damaged.
Registered User
Joined: Mar 2023
Posts: 2
Likes: 0
The light green wire is connected to the power side of the high beams circuit. It's set up that way so that when the high beams are on there's no ground for the fog light relay and the fog lights will be off while the high beams are in use.
Applying power to the light green wire through a test light should illuminate the test light bulb and may or may not also illuminate the high beams depending on how much current can flow through test light to the high beams. It's an electrical impossibility for the test light to pass power to the high beams but not illuminate itself because the power has to flow through the test light bulb to get anywhere. That's assuming a good old fashioned test light rather than one of the fancier new electronic ones.
In any case, if you got to step 5 in the list, just skip it and try swapping the horn relay into the fog light socket and see if the lights work. That whole diagnostic procedure I listed was more about proper diagnostic steps than it was about quickly determining the cause of the problem. In practical terms the list should have been: 1. Swap the horn relay into the fog light relay socket. If it works then the relay was the problem, otherwise start checking wires as described in the original list. It's much more likely that the relay is the problem than the wiring unless you have reason to suspect the wiring might be damaged.
Applying power to the light green wire through a test light should illuminate the test light bulb and may or may not also illuminate the high beams depending on how much current can flow through test light to the high beams. It's an electrical impossibility for the test light to pass power to the high beams but not illuminate itself because the power has to flow through the test light bulb to get anywhere. That's assuming a good old fashioned test light rather than one of the fancier new electronic ones.
In any case, if you got to step 5 in the list, just skip it and try swapping the horn relay into the fog light socket and see if the lights work. That whole diagnostic procedure I listed was more about proper diagnostic steps than it was about quickly determining the cause of the problem. In practical terms the list should have been: 1. Swap the horn relay into the fog light relay socket. If it works then the relay was the problem, otherwise start checking wires as described in the original list. It's much more likely that the relay is the problem than the wiring unless you have reason to suspect the wiring might be damaged.
Last edited by WS6_2001Bird; Mar 17, 2023 at 06:43 PM.