Intermittent fog lights and not a bad light switch

[ron.in.irvine]

1997 Boxster 107K miles

Sometimes I can switch on my fog lights and other times I can't - that includes both the front fog lights and rear fog light. This is a recent problem and all of the other lights and electrics seem to work fine.

I've replaced the fuse (#A7), relay (#12), and lightswitch and things haven't improved. I've noticed that they seem more likely to come on if the car has been sitting in the cold and less likely to come on if its been sitting in a warm place. Sometimes if they haven't come on but I've left the switch knob pulled out I'll notice that they've come on while I've been driving but they won't necessarily come on again after a re-start.

After replacing the switch and discovering the lights still wouldn't come on reliably, I finally got around to looking closer and I've discovered that with the ignition switch on there is 0 voltage at the A7 fuse. Looking at the wiring diagram for the car it would seem that there's really nothing much upstream of the fuse that could cause that without also effecting other systems.

Anybody know what I should be looking for?

[Loren]

Do you mean the headlight switch?

If so, then start you likely need to look for bad grounds.

[ron.in.irvine]

Yes, I do mean that I replaced the headlight switch and relay #12. When the front foglights don't come on, the rear foglight doesn't come on either. Which sort of suggests not a ground issue as they don't share a common grounding point (so far as I can tell in the wiring diagrams).

Here's how I understand the flow of electricity to the front foglights:

Current distributor (80A fuse) --> Relay Term XE (off at start) --> A7 fuse --> headlight switch --> Relay Fog Light (off when high beams on) --> front fog lights.

Flow to the rear foglight is exactly the same up to the headlight switch after which point it flows back to the tail light assembly (bypassing the fog light relay).

Note that I've now also changed the XE relay (#9). As the foglights and the cigar lighter both come off the XE relay and the cigar lighter works, I'm guessing that the relay was fine but I changed it anyway. Which I think leaves only something between relay #9 and the A7 fuse as the failure point - and all of that stuff would seem to be within the fuse panel and/or relay panel.

I do see that there is a Bridge Plug (#24) which says it has something to do with fog lights, but I don't see any mention of it on the actual wiring diagrams - and I don't know what bridge plugs are anyway. Jumpers? Fusible links?

While I hesitate to think that a wire broke or a connector failed, I don't have many alternatives left to consider.

Ideas?

[Loren]

I would suspect the connectors before wiring unless the car has been in an accident.

Sometimes the pins on the fender connector where you push the headlight into get pushed out of their connector damaged. I've even seen that connector broken and work sometimes.

[EleCTriCT]

+1

definately check the connectors in the fender.... the next time the light (s) go out you can even try pressing the headlamp further in and see if it comes on and thats a dead giveaway...

I see problems with the connector at the back of the headlamp VERY often

[jflash]

Ron.in.irvine,

I was wondering if you have solved your Fog Light problem?? I have the same issue and have gone through the same steps as you (fuse, relays, new light switch, no 12 volts at fuse A7) I did go one step further and applied a 12 volt source to the A7 fuse holder and the fog lights did come on which eliminates everything except the 12volts source to fuse A7. Any help would be appreciated.

Thank You,

Jack

[wvicary]

Also inspect the contact in the fuse block that engages the blade of the fuse. They can corrode or overheat and cause intermittent issues.

[jflash]

Thanks wvicary,

I have done that already and cleaned the contacts with no luck.

Jack

[jflash]

Here is the solution to my Fog Light Problem:

As I said earlier the A7 fog light fuse was not getting 12 volts. This 12 volts source is an output from Terminal XE Relay #9. I found that the Relay #9 female connection at pin 87 was not making good contact. After tightening up the female connector the fogs are now working. I wanted to send this info on. Maybe it will be beneficial to someone else that has a Fog Light issue.

Thanks,

Jack

[wvicary]

Thanks for letting us know.