Help with headlight problem on mustang

[Busaman5000]

I have a 1999 Mustang GT Convertible that I just bought that as some of you know. A couple of nights ago while driving home from work my headlights blinked on and off. I thought this was weird but didn't think much about it.

Tonight however, my headlights went off and stayed off while driving home from work at midnight. But here's the weird thing...

Both my hi beams and low beams both would not work. But if I pulled the switch back to use the "flashers" the highs would come on and stay on as long as I manually kept the switch pulled back the whole time. If I just used the high's normally nothing worked. How ever halfway home my lights popped back on and magically started working again.

My fog lights, running lights, blinkers etc.. all work just fine its just my headlamps.

I checked all the fuses. They seem fine. Any ideas?

 

[dadofthree]

You're taliking about the turn signal switch ? I goes bad, and has to be replaced. I've seen this happen on cruisers before.

 

[Busaman5000]

You're taliking about the turn signal switch ? I goes bad, and has to be replaced. I've seen this happen on cruisers before.

Well the turn signal switch controls the high beams but there is a pull out switch on the dash that turns on the low beams and running lights. Could that be the culprit? But if it was faulty wouldn't my running lights not work also?

 

[Busaman5000]

I wish they didn't come back on. Its almost im possible to diagnose the problem while they are working.

 

[dadofthree]

Which switch were you holding to get the lights to work ?

 

[Busaman5000]

Which switch were you holding to get the lights to work ?

The turn signal switch. You just pull it back and let go to flash the high beams, push it forward to turn the high beams on.

The high beams worked when pulled back to flash. Would not work when pushed forward to turn the high beams on. But the low beams would not come on at all.

 

[dadofthree]

Replace the turn signal switch. I've had several cruisers with similar issues and that was the fix. Could be something else but just think about what you are writing. If I manipulated this switch they worked, etc.

 

[Projekt]

Try the headlight relay it could be getting hot and opening the circuit only to close the circuit when it cools off.

 

[Projekt]

The turn signal switch. You just pull it back and let go to flash the high beams, push it forward to turn the high beams on.

The high beams worked when pulled back to flash. Would not work when pushed forward to turn the high beams on. But the low beams would not come on at all.

Based on this scenario it is definitely the headlight relay because the flash to pass function is a direct function of a high power circuit built into the flasher/indicator selector switch.

 

[Projekt]

The "pullout" switch gear you mention provides an ON signal to the headlight relay in order to enable power to the lights. If the relay is faulty it behaves exactly how you described and will not hold the ON/enabled position.

 

[proud dad]

The turn signal switch is a multifunction switch [has more than one job]it can cause the headlights to go out.This is normal on a Ford to act this way when the switch fails.
If I had a dollars for everyone I replaced on the job I'd take next week off

 

[proud dad]

whoops

 

[Projekt]

The turn signal switch is a multifunction switch [has more than one job]it can cause the headlights to go out.This is normal on a Ford to act this way when the switch fails.
If I had a dollars for everyone I replaced on the job I'd take next week off

Come to think of it, I've done the same.

 

[Busaman5000]

Ok so we have narrowed it down to the headlight relay or the turn signal switch. I will try changing the relay first being its the cheapest and easiest to do.

Thanks for the help!

Leave it to the org for help. I posted this on mustangforums.com at the same time and didnt get a single reply. lol

 

[Projekt]

Ok so we have narrowed it down to the headlight relay or the turn signal switch. I will try changing the relay first being its the cheapest and easiest to do.

Thanks for the help!

Leave it to the org for help. I posted this on mustangforums.com at the same time and didnt get a single reply. lol

I believe there are a few relays on the car that are the same capacity as the headlamp relay. Also, you could try to test the relay before replacing it.
There is a little schematic on most relays that help to give you an idea of which post to apply 12V to and then check continuity across the other terminals.

 

[Zoinks!]

According to the service manual wiring diagram, that car uses the multifunction switch for the relay. The fog lamps use a relay, but the headlamps use the multifunction switch (turn signal switch) I've attached 2 schematics. One is the wiring diagram for the headlight circuit on that car, the other is the buss center I.D. The buss center is off a 95, but I don't think anything was changed, unless yours has DRL's. The circuit schematic you'll have to save and then zoom in on to see. It's clear once you zoom. Notice in the buss center I.D. there's no headlamp relay.

 

[twotonevert]

Try the above and see what you come up with. Also, mustangs, especially fox bodys, were notorious for ground issues. Make sure all the engine grounds and leads are clean and intact. My car had all kinds of electrical demons before I corrected the grounds.

 

[Projekt]

According to the service manual wiring diagram, that car uses the multifunction switch for the relay. The fog lamps use a relay, but the headlamps use the multifunction switch (turn signal switch) I've attached 2 schematics. One is the wiring diagram for the headlight circuit on that car, the other is the buss center I.D. The buss center is off a 95, but I don't think anything was changed, unless yours has DRL's. The circuit schematic you'll have to save and then zoom in on to see. It's clear once you zoom. Notice in the buss center I.D. there's no headlamp relay.

Well that says it all!

 

[Zoinks!]

Try the above and see what you come up with. Also, mustangs, especially fox bodys, were notorious for ground issues. Make sure all the engine grounds and leads are clean and intact. My car had all kinds of electrical demons before I corrected the grounds.

Good advice here, but if the 99-04 cars are the same as the 94-98 cars (which I'm pretty sure they are) all the exterior lighting is grounded at the same terminals. They're located on the radiator core support on both the left and right sides. The right side ground terminal broke on my 98 gt and I had ALL KINDS of issues with the high beams, low beams, turn signals, and tach (it's grounded there too). So I don't think that would be the issue in this case, however you may still have grounding issue on a single circuit somewhere. But from what you described I'd agree with what most others have said, and say you've got a multifunction switch issue. They are notorious for goin out on mustangs and other vehicles that use that same switch.

Still good advice by twotone. Ground issues can keep you runnin in circles for a long time, and are always a good starting point after fusses and relays.

 

[GIX1000_07]

The only true fix is to get a chevy. Some one had to say it