Headlight issue - 2001 Mustang

[MrA79]

GF's car - lately the headlights have started cutting off\back on after driving for a bit. Not sure if it's just the low or both low\high, haven't had the opportunity to test that. If you kill the lights and turn them back on (in-dash pull out switch, not part of an arm) they stay on for a few minutes and then go back to blinking. Seems random tho, as occasionally they'll stay on after turning the switch on\off a few times.

Obviously this is ridiculously dangerous, but I'm not really sure where to start troubleshooting. Does it sound like a short in the switch? Something else? Thanks, auto geniuses

Edit - if it helps, the blink seems to be a pretty constant interval, almost like you were flashing your lights

Thread necro-ed by a newbie, closing.
Zenmervolt - AnandTech Moderator

 

[exdeath]

Switch, fusebox, or the connector at the bulb housing.

Since each light has it's own independant fuse/relay and both lights are doing it at the same time, I say it's the switch.

Though sounds like it could be a malfunction in an anti-theft/valet module or something?

 

[LTC8K6]

Circuit breaker tripping?

 

[LTC8K6]

There's a headlamp relay under the hood.

It's a Maxi Fuse, not a relay.

 

[SpatiallyAware]

The fact that turning them off/on makes them stay on for a bit makes me think headlight switch.

She needs to figure out if it's both headlights, also if taillights go off as well.

 

[SpatiallyAware]

Circuit breaker tripping?

wtf...

 

[MrA79]

The fact that turning them off/on makes them stay on for a bit makes me think headlight switch.

She needs to figure out if it's both headlights, also if taillights go off as well.

It's both headlights, I think the taillights go as well but I'll confirm.

Thanks for the input! Switch shouldn't be too hard to replace, hopefully.

 

[CrackRabbit]

The fact that turning them off/on makes them stay on for a bit makes me think headlight switch.

She needs to figure out if it's both headlights, also if taillights go off as well.

I would guess the switch as well. Have you tried adjusting the brightness of the interior lights to see if that effects anything.
I had an old Tempo that wouldn't turn on any of the lights unless the rheostat was in a certain position.

 

[MrA79]

I would guess the switch as well. Have you tried adjusting the brightness of the interior lights to see if that effects anything.
I had an old Tempo that wouldn't turn on any of the lights unless the rheostat was in a certain position.

Tried that and turning on the dome light (same switch) - didn't have an effect

 

[LTC8K6]

wtf...

Cars often have thermal CB's on high amp circuits.

They can "blink" sometimes as they heat up and trip, and then cool off and close, etc.

However, there isn't one in this case.

There might be a DRL module though.

 

[LTC8K6]

I would bet DRL or GEM module.

 

[phucheneh]

It's probably not the switch if you can't wiggle or otherwise manipulate is and cause a problem.

Relay would be a good guess. When a little solder joint inside cracks, it can be pretty intermittent.

But it could also be wiring. Or just generally some kind of loose/poor connection. If it's both lights, at least you've eliminated part of the circuit. Start with the fuse and relay and work back towards the lights.

Is a 2001 Mustang multiplexed (CAN)? I would think the headlights are pretty simple, but if there's a module controlling them, that could certainly be it as well. If the headlight switch is not going directly to said module...well, good luck, that would be shitty to troubleshoot. e.g. headlight switch is connected to BCM, BCM has digital communication with a DRL module or something. But I really can't recall those Mustangs being that complicated.

 

[LTC8K6]

Don't forget the multi-function switch. It controls the high beams and may cause headlight problems.

 

[MrA79]

Update - tail lights also go out in sync with the lowbeams. High beams seem unaffected. Ran it past my normal mechanic and got a response along the lines of 'that's gonna suck to fix, we'd probably have to go one piece at a time until we got lucky' - aka huge labor costs.

Thinking it might be time to dump the 'stang and get her something else

 

[exdeath]

Shouldn't be too difficult to find something affecting all lights at the same time...

Alarm system, hazard switch, a body control module/GEM box, or any associated harness junctions, etc. Especially since you can reproduce at will.

 

[MrA79]

That's the problem - I can't reproduce it at will. Just have to wait for it to start happening and then check stuff like the tail lamps etc. Doesn't seem to follow any pattern ie amount of time they're on, switch positions etc.

No aftermarket alarm, just the normal Ford anti theft. Hazards are a different set of lights/switch, didn't think to check those out. Not a circuitry wiz, sadly.

 

[LTC8K6]

The headlight switch doesn't cost that much. I'd try that first. Look at the switch and the harness/connectors. See if there are signs of overheating, or signs of deterioration/corrosion.

 

[mvbighead]

Update - tail lights also go out in sync with the lowbeams. High beams seem unaffected. Ran it past my normal mechanic and got a response along the lines of 'that's gonna suck to fix, we'd probably have to go one piece at a time until we got lucky' - aka huge labor costs.

Thinking it might be time to dump the 'stang and get her something else

What? Flickering lights is cause for dumping an otherwise ok vehicle?

If she is otherwise happy with the vehicle, I can't see this being a major expense to fix. Just time to track it down.

As it is, this forum has a lot of good info:
http://forums.mustangworks.com/f8/h...y-change-light-switch-need-small-advice-1685/

Seems to be a lot of talk about the relay, as well as the use (or lack there of) of halogens may cause overheating, indicator switch, etc.

To me, this sounds about like a 50-100 dollar problem, tops. Not that I normally advocate dealer mechanics, but if you have a trustworthy Ford dealer to work with, they might know of some specific things common to that model. Worth a shot maybe.

 

[MrA79]

I'll check that out, thanks much. Flickering wouldn't so much be a problem, but they cut completely off - very dangerous at night in a semirural area.

 

[mvbighead]

I'll check that out, thanks much. Flickering wouldn't so much be a problem, but they cut completely off - very dangerous at night in a semirural area.

I guess I get that too. My only point being that this doesn't seem to be an issue that is going to be all that terrible to fix.

If you don't want to deal with the problem, I'd suspect a dealer would have a good idea as to what might cause that, and I wouldn't think they'd charge much more than a few hundred to correct it. Obviously, it's going to be cheaper to replace some of those circuits/relays, but that part is up to you.

Long/short of it is that something like this shouldn't be a costly fix like a heater core replacement, transmission, or head gasket. And as there are a few parts mentioned that are in the 10-40 dollar area, you could throw some new parts at it to try and make it go away. If all that fails, at least you'll have crossed a few things out so the mechanic can go looking for other things.

All in all, I don't really suspect that the few things that can be changed cheaply would be difficult for even the greenest mechanic to swap out.

 

[phucheneh]

Update - tail lights also go out in sync with the lowbeams. High beams seem unaffected. Ran it past my normal mechanic and got a response along the lines of 'that's gonna suck to fix, we'd probably have to go one piece at a time until we got lucky' - aka huge labor costs.

Thinking it might be time to dump the 'stang and get her something else

Get a new mechanic. It's called 'diagnosis;' you use it to avoid having to just replace parts until you 'get lucky.'

You probably CAN reproduce the problem if it's happening fairly often. There is probably a part somewhere that you can tap, or a harness you can shake to get the lights to flicker. Just gotta find it.

Here, you'll probably want these:

http://3.7mustang.com/vb/attachment...ram-headlight-switch-2001-exterior-lights.pdf

http://3.7mustang.com/vb/attachment...-diagram-headlight-switch-2001-headlights.pdf

So the park lamps and headlamps both go out, right?

It looks like the lights are all power-switched, and they don't share common grounds. There, you've already eliminated a possibility.

Then you've got the fact that they're on different fuses...appears there's no headlamp relay (assumably solid state DRL module instead), park lamp relay doesn't share wiring with headlamps...you know it's not the wiring near the lights, as a broken circuit wouldn't cause a loss of power to the lights at the other end of the car...

The high beams not going out might be a very important fact, but I don't have time to really scrutinize the wiring diagrams right now.

There are DRL's, right? Do they ever go out, or does it only happen when the headlight switch is actually turned on?

 

[LTC8K6]

The switch is like 15 bucks at Rock Auto...it turns on both the headlamps and tail lamps. Seems a good initial candidate.

 

[phucheneh]

It would affect the high-beams, too. If he's SURE the highs are not being affected, it would look to me to be the DRL module (or its ground/power supply wiring), but it's hard to say because that diagram doesn't appear to show DRL module outputs, just sensing wires (unless Ford has a different definition of 'in').

Now that I look a little more...it doesn't look like the parking light and headlight circuits are associated at all. While the 'headlight' position' also turns on the park lights, there are seperate contacts inside the switch.

Only link is DRL module, which I assume can control both. I'm not sure why its outputs aren't drawn, though...I guess there's a seperate 'DRL' diagram.

 

[LTC8K6]

Does the DRL module affect the tail lights? Those are going out also.

 

[phucheneh]

Does the DRL module affect the tail lights? Those are going out also.

Not the stop lamps or turn signals. But don't DRL's use parking lights?

Like I said, it would help if I could find a diagram of the DRL outputs and/or some explanation of its functionality. I'm just guessing here, since I don't see anything else to tie those circuits together.