My headlight doors open when I turn the switch to position one for parking/fog lamps. This is intermittent.

I have replaced the headlight switch in the dash, and now the headlight control module under the hood.

Doors still open when they shouldn't.

My mechanic wants to replace both headlight motors, but they are working, so it seems to me something else must be the cause.

What is the proper way to diagnose this problem (instead of throwing money at it)?

 

I had this happen on my 1990, but the culprit was an aftermatket Daytime Running Light modue that I had purchased and installed on the car - it tapped into the headlight relay (under the hood on the drivers side at the front of the car on the frame - iirc). Worked fine for a while, and then shorted out or something. So that would lead me to check the headlight relays.....

 

I have no after-market equipment, but it does seem logical that there is some wiring/connector/short issue. Not sure what "relays" you mean, but the control module that was replaced is in the location you describe.

AFAIK, the motors are simply mechanical, and should get power from the module at the proper time. But the mechanic is telling me something in the motors gives feedback to the control module.

Not sure what to believe.

 

his 90 and your 95 are two completely different systems, his has three relays , yours has a headlight control module, you need to take it to a shop that does diagnostic instead of parts throwing, A multimeter is your friend

 

So, since the switch and module have been replaced, you agree that there is some wiring or connector issue --- and that replacing the motors is unnecessary? (Unfortunately, the word "multimeter" makes my head hurt!)

 

if it was only one side that did it , possibly the motor, both sides doing it , its a wireing issue

 

How often does it do this. Is it often enough that you can troubleshoot it or is it just a "Use the Force" kinda deal. Since both motors are doing it, it would appear that there is power getting to the relay inside the Headlamp actuator module. This relay that opens the doors needs 12 volts to open the doors so a ground problem likely isn't it.

You have got to get 12 volts onto the yellow (#10) wire to open both doors. That wire comes from the headlight switch that you've already replaced and it makes a stop at the dimmer switch before it goes straight to the module.

Nothing on the output side of the module can cause your problem. It's highly unlikely that there is an intermittant 12 volt wire touching the wrong place so my GUESS would be the dimmer switch.

It looks like you could find the 2 yellow wires going up the steering column to the dimmer switch and just disconnect them and put them together. You'd lose your dimmer but you may find the problem. Just another idea that may or may not work would be to leave you dimmer switch in the Hi beam position and see if the lights open. The next day leave it in the Low beam position and see if the lights open.

With any luck it'll do it in one position and not the other and that would tell you that the 12 volts needed to energize the relay in the headlamp control module is being generated by the dimmer switch and that would lead me to believe the switch is faulty.

It's sort of hard to diagnose over the internet but that's how I would start. No meter required and save that headache.

 

Guys, thanks for the input.

The problem happens most of the time. Sometimes it stops after the car sits for a couple of days, but as soon as I turn on the headlights all the way, the problem begins happening again.

Yes, both doors open when they should not (first dash switch position). So I agree it must be a wiring problem (as opposed to motors).

I will investigate the dimmer switch position today.

 

Very interesting --- but what does it mean?

So I tried the high-beam low-beam thing this morning, but it had no effect.

You called this the dimmer switch, which made me think of the dimmer switch for the interior lights. When returned home, I turned off the engine and turned the dimmer switch all the way on, then turned the headlight switch to the fog lamp position.

The doors stayed closed! Now they are working properly no matter what position the dimmer switch is in. (I'm sure this will not last.)

But what does it mean? I assume this switch is part of the whole headlight switch that was just replaced.

 

lesse....... what does it mean? The meaning of lites not working like they're s'posed to....I bet you're gonna find out what post #4 means too.

 

@DaveP85C4

I believe all lights, in and out, function properly. No dim lights. I'll have to check whether side and front function together when turn signal is on.

To be clear, what is the "dimmer switch" you are referring to and how would I disconnect it? (Dimmer = high-beam switch on steering column, OR interior light dimmer on dash headlight switch, OR something near the headlight units?)

 

Here is a possibility. You say that you replaced the headlight switch. Where did you get the replacement? It's possible that the replacement switch is faulty.

Rather than throwing more parts at the problem you need to take this to a shop that workes on corvettes and have them test the various connections with a multimeter to determine where in the circuitry the problem lies. The multi meter simply tells you if voltage is flowing through a connestion and what the level of the voltage is.

You can purchase the 2 volume factory shop manual which contains all of the electrical schematics buy an inexpensive multi meter and test the connections yourself.

 

Here's the door motor schematic from a 1995 FSM. To get the doors to open you must energize the relay in the actuator control module. After they are open the module will break the return (ground) and turn the motor off. To energize the relay you've got to have 12 volts on the yellow wire (10) on the module. It gets it's power via the HEADLAMP dimmer switch. Something in the headlight dimmer switch could be broken/shorted and supplying 12 volts to the yellow #10 wire. That would energize the relay in the actuator control module and open the headlight doors. That's what I meant when I said try the "dimmer" in the other position. If you've been leaving your lights on "HI" when you turn the lights off or if you've been leaving the lights on "Lo Beam" when the switch is off.

Try that switch in both positions and see if the lights come on in either Hi or Lo or both. If it's one or the other then the switch may be supplying the voltage and that's not right and would indicate a faulty switch. IMHO

 

@1963SS

This is great! Well, OK, I'm an electrical dunce, but I will take this to the appropriate person to diagnose the problem --- instead of throwing parts (and my money) at it. Now I know how to approach the problem.

The headlight dimmer switch position had no effect, but I will test again today. And I'll also try the interior light dimmer switch when the problem happens again to see if it's a repeatable temporary solution.

It may be a while before I can get back to a shop with this.

Thank you.

 

I think.... that someone previous to you...connected a wire of your headlite circut to something else and didnt do a very good job...intermitant usually means a contact.... is making and breaking , contact...either with itself or a ground...somewhere. It doesnt take a vette specialist to chase wires...it does take someone who understands wire diagrams and electrical flow. Where a vette or even chevy specialist would be an advantage , would be that they could probably look at your car and instantly realize what isnt right. but I dont think you need that. you need someone who can look at two wires , see they're different colors, and ask the question ....why . Since your not doing your own work, you need to see an 'auto electrical' shop. hope this helps. btw if you have an after market stereo, that you didnt install or an aftermarket alarm system or for that , any aftermarket electrical part, turn it off and see if the issue fixes itself

 

Mine is doing the exact same thing. Was in an accident and front bumper was replaced. Hood and such needed repaint, so headlight assembys came out.

Ever since, headlights pop on parking light setting and motors run longer then they should.

I am thinking it is a loose/non-connected groud for the headlights.

Does anyone know where this is located?

TO the OP: I hope you figure it out, i think we will have identical solutions.

Mike

 

Where the frame extends past your radiator. on that rail is a bolt with wires attached, you'll need to raise the hood.

 

If you have an aftermarket radio (or if it had one before you got the car), I would look very closely at the wiring there. Someone may have incorrectly tapped into the circuit that turns the radio back lighting on when you turn on the parking/headlights. Same goes for an alarm.

 

Any update on fixes? I'm trying to locate the headlight relay on my 91 without much luck...

Thanks,

Mike

 

Sorry, I have not had time to leave the car with a shop to re-diagnose. Just living with the issue for now.

I did find a broken ground wire on the right side and reconnected it to a bolt near the front of the radiator, but that had no visible effect.

I will post here when I get around to solving this.