Fog Lights & Generator Light

[hdavis]

To all electrical gurus,

I hardly ever use my car at night, and today when I truned on the fog lights, the gererator light would come on, but only slightly, not full intensity. I checked the wiring and it looks OK, any ideas?

[Gearbox]

Sounds like the additional electrical load causing the alternator light to flicker on may suggest a weak alternator. It's still putting out enough to sustain normal operation, but soon as the another accessory starts to drain the power, the alternator falls below it's specified normal running range. I would also check to see if the batteries are in good condition and what the output is for the alternator for both volts and amps. Test when the car is running with no accessories on, then turn everything on and see if the drain effects anything. Good luck Allan

[Zithlord]

I am no expert but have read that bad ground connection/straps can cause this?

John

[70SATMan]

I agree with John,

When was the last time you checked your grounds? Also, if factory supplied fogs, you have ground wires inside your fog lights. Check those connections too. Does the alt. light come on going from low beam to high beam on your headlights?? You are going to pull more juice going to high beam than adding fogs when you are on low beam.

[hdavis]

Thanks Guys,

I checked the grounds yesterday, and they seemed OK, these are factory fogs. I will check again on the weekend with more time.

The alternator suggestion is good, I will also check that. I hope it's a ground and not the alternator, and since the high beam does nothing to the alternator light (I'm running H1s), it could be a faulty ground.

[Gearbox]

Yes, a faulty ground could possibly cause this, but I took HDavis' initial post at face value when he said he had gone through the wiring. Thus the difficulty of diagnostic work over the internet. But an easy way to test this is to attach a set of jumper cables to the engine and ground it to the body, if the light still comes on, it's not the ground.

I assume the head lights are on, car running, and when the fog light is turned on, the alternator light comes on. Let me know if this is correct. This would indicate the additional load is not overcomed by the alternator and battery which is a sign of insufficient amps. The way the system works is that the battery acts like an electrical shock absorber between the alternator and the accesories. The factory manual warns not letting the alternator power the car by itself as it may damage the alternator. And the light indicates that the electrical drain is overpowering the charging system. So do a load test on the battery and test the alternator for volts and amps. The battery should read 12-13 volts with the car off, and around 14 volts when running.

Now if the head lights are off along with every other accessory on the car, and the fog lights are the only accessory that causes the light to come on, you may have a fault to the fog light system. The fog lights should not drain much more power than the headlights. If you can take an amp reading inline with the fog light wires to see how much amps the lights are drawing when turned on, that should tell you if there is a problem. Compare this with the amp draw of the headlights. If your reading is way too high, it's the fog lights. Pull the bulb out of both lights, disconnect the battery and see if you get any continuity with the power wire and ground. If so, trace the wires until you find the short and then check your fuse to see why it didn't pop. If good, then check you fog light grounds. Also now is a good time to clean all the connections and sockets with dielectric grease. If all is good, last resort is to swap out the bulbs. yeah, I know it's a long shot, but you never know.

Now if you are still with me and not bored to tears yet, the reason I think this may be related to the charging system if you did determine all is good with the wiring is that when the alternator fails, it generally will fail in steps, the diodes are usually the main suspects and you have multiple diodes in the alternator. You can have multiple diode failures, but I have seen alternators run with only one operational diode, albeit producing just enough current to run the car, barely. I have also seen bad batteries that are sulfated that takes on a surface chrage of 12 volts (enough to start the car), but soon as it is stressed, it discharges to 6 volts in a matter of seconds, thus causing additional drain on the alternator to charge it back up again. I truely hope it's something simple, but you are not going to know until you exhaust the possibilities. I apologize for being so exhausting, Good luck Allan

[boxster03]

My best guess would be battery related. New batterys will work wonders.

[hdavis]

Thanks Allan, my Saturday was looking a little slow, but not anymore.

This indeed happens with the car running and headlights on, the alternator lamp glows when the fogs are turned on. As I said, I have gone through the wiring, but at night, so I guess I could do a better job and actually clean and lubricate everything vs. just verifying nothing was loose.

I will go throug everything you suggest on Saturday, and that should set the issue straight, as you say, exhausting but very comprehensive.

[hdavis]

My best guess would be battery related. New batterys will work wonders.

Could very well be, my battery is about 3 years old, maybe it's time for an Optima.

[Gearbox]

Hoping for a sunny warm Saturday in Mexico. BTW can you switch the fogs on without the headlights? This might speed you along, or at least verify your suspicions. Good luck and let us know how it turns out, Allan