Does anyone know the most common cause of a headlight door not opening? Some history, since I painted the car, the driver's side headlight door would hesitate when called upon. Sometimes it would take a bump or two to pop open. I thought it was getting hung up on the paint. Now it won't come up at all.

I searched headlights, but didn't find anything helpful. They blamed most problems on bushings, which I don't think applies. Upon checking the FSM I read "If one HEADLIGHT DOOR is not operating..." and recommends a series of voltage checks. It goes on to say if all voltages are correct, replace HEADLIGHT DOOR RELAY". Is this correct? All voltages were correct at the relay. I have correct voltage going into and out of the relay at the correct time (switch on/off). It goes on about checking voltage to the HEADLIGHT DOOR MOTOR which were all correct also. I guess I haven't checked the ISOLATION RELAY yet but this is all greek to me.

I also need to know the best way to get the relay off the backing plate and how to get the plug out of the relay without damage.

Any help with this will surely make my life easier.

 

Well mines an '86 but I would think they're similiar. The relay just slides down the backing plate to a point and then you lift it out. Can be a little hard but it does just slide one way and then lifts out. The relay has two clips on either side that you slide down the guide of the backing plate until you get them to the larger opening in the guide and then they lift out of the backing plate. Then the plugs should have a clip on either side and if I remember correctly you depress the clip and pull the plug out of the relay. I went through a lot of hassle and finally found my problem to be in the weather pack plug from headlight to wiring harness. It was very tempormental on how it had to be plugged in. Actually found my problem when I did not seat the plug all the way, kinda like not plugged in all the way and it started working. When I would seat the plug all the way, the voltages were incorrect. Since you said it works sometimes after a few bumps in the road I would be checking all connections. You can also swap the relay from the working passenger side to check if the relay is your problem. It might also be internal in the motor. There are contact points inside that wear down. If it does work sometimes and move all the way to the open and closed position I would think your gears inside the motor are fine.

On another note, if it is getting caught on the opening you need to readjust the painted top so it does not touch anything on its full travel. But even if it was getting caught I would think you would hear the motor trying to open. Do you?

 

I will try switching relays. It USED to open sometimes, but stopped altogether now. Thanks for the tip. I'll let you know if that works.

Glide

 

On they '85 you don't have the wearable bushings what you have is a nylon gear with two rubber pads in it. My '85 had a headlight start winking earlier this year so I tore apart the motor. And replaced the gear. I posted a bit of a rant about it here.

 

Many years ago I replaced the two gears in the drivers side headlight on my 85. The new gears did not come with the rubber shock absorbers in the large gear, so used the rubbers from the original gear. Worked fine for several years then the drivers light headlight was having trouble coming up and going down until it just quit doing anything. Took the headlight out and opened up the motor thinking the gears I had put in were destroyed. Surprise, surprise. The rubbers in the big gear had gone soft and were mangled in the gears. Cleaned it all up and assembled the motor and headlight and put it back in my 85. Left the headlight disconnected to it would not be used while I searched for new rubbers. I am still looking for a source of the rubber shock absorbers. Don't drive the 85 much anymore, so it is not a time critical hunt.

 

Couldn't you make them?

 

Just pulled out my Fall/ Winter 2007 C4 Catalog, and it shows the gears with the rubbers for $21.99 ea. I would call and make sure the rubbers are included before ordering thought. (Did you ever notice that when your writing C4, if you forget to let off the shift key, you get C$! I'm not so sure that is purely coincidence!)

 

I ran all the voltage checks again for this inoperable LH headlight door as described in the FSM. All voltages are correct EXCEPT the red wire from the isolation relay is hot all the time (SB hot only with lights off). But the voltages are correct at the door motor. I don't see how that could make it not work since voltage at motor is cortrect. Do I need a motor? Don't see any movement or hear any gears grinding. Can it be bench tested?

 

Blownfuel1, what catalog did you look at for 2007?

Glider, recommend you remove the headlight assembly and take the motor apart and check the gears. It is really an easy operation, remove the headlight cover first, and then the bolts that disconnect the headlight frame from the hood, course disconnect the electrical connections. If you have to buy new gears and they come with new rubbers sell me your old ones. I wish I could make some new ones.

 

Looks like that is the next step. Then I'll be driving around for a month with a hole in my hood.

I wish I could just sell it and get a 96 LT4, really. I found the one I want but wife won't let me get until I sell the 85 and my dump truck and my boat.

Thanks,
Glide

 

Did you switch relays yet? I had the same problem, my headlight would open when it felt like it, then it stopped.

Switching relays caused the inoperable headlight to work all the time, and the operable one to cease. 60 bucks for next day shipping and a new relay.

Honestly, it wasn't that hard to troubleshoot that either, 30 minutes tops while I figured out how to remove everything from the wheel well.

 

I switched relays and the problem was the same. Since the red wire from ther isolation relay is hot all the time (SB hot only when lights are off), I could try replacing it before I open up the motor. My problem with that is the isolation relay controls the RH door and my problem is with the LH door plus voltage is correct at LH motor.

Anyone know how to bench test the motor when its out?

Thanks!
Glide

 

I've had headlight problems for years on my '85. These headlight operate on relays and limit switches inside the motors. When the headlights hit the stops, whether going up or down, there are contacts that open and close. This opening and closing of switches redirects the current flow through the motors causing them to rotate in the opposite direction. It's difficult to explain unless you have a schematic diagram. Sometimes just removing the motors, dismantling them, and cleaning the set of contacts in the motors with emery cloth is all that is needed to restore headlights in operating condition. The voltage checks that are in the FSM are a good guide in determining if the relays are working properly. Something that is overlooked is that when the motor contacts are working properly, the voltages that are read at the relay wiring rely on these contacts opening and closing properly. So just because you don't get a correct voltage at the relay harness that doesn't mean the relays are bad. It could be the contacts in the motor are dirty and not allowing the current to flow to the terminal that requires a voltage reading. I'll see if I can find a link to one of my old posts. It was lengthy but explained how the system operated. Something else to keep in mind is that simply reversing the voltage on the motor to see if it works is not a good test. These are 3 wire motors. The polarity of the voltage is reversed in addition to two of the wires sharing the circuit for negative 12 volts. Its a very interesting system, confusing at first to understand but once it is it makes sense how the system works. It was only after 160,000 that the motor contacts, like points, wore down to nothing so that no current flowed that I upgraded to the later model headlight motors. This is an option but should only be considered if all else fails. These 3 wire motors can last a long time.

Art

 

I'd like to also add that if bumping or pushing slightly on the headlight, or rotating the manual **** slightly causes the motor to rotate then that is a very sure sign that the limit switch contacts are dirty. Bumping or pushing on the headlight forces torque on the motor. This is the same torque that is applied when the motors hit the stops. When the motor stops torque is applied and the motor armature slides in some blocks forcing one set of contacts to open and another to close. Bumping or pushing on the headlights isn't going to make the contacts in the headlight relays operate, it just gives the current coming from the relays a path to follow in order to open or close the headlight.
Here's a link to an archive post. It also has a wiring schematic in one of the posts. If you want to see more archive threads on this do an advanced search with headlights as a key word and my username mrrenoman to find more threads I've responded to. Some are are more detailed than others.
http://forums.corvetteforum.com/show...ght=headlights

Here's an excellent website with pictures on headlight repair. Click on the pictures to enlarge them.
http://automobiletest.com/service/19...ghts/index.htm

Art

 

Excelant informatoin Art. I will remove and clean motor today, then reportback. Thanks for looking!

Glide

 

Use your advanced search function at the top of the page. Theres hundreds of posts on how to fix with photos. Save yourself time and get the correct info from members who have had the problem and fixed it.

 

Just a quick "thank you" to everybody (especially Mr Renoman) for helping me solve my headlight problem.

Took the motor apart, cleaned it up, put everything back together and it works like new. The contacts in the motor needed a couple swipes with a piece of sandpaper.

I am now authority on early C4 headlights...along with every other part that i've fixed on this project. The C4s are so easy to work on, with "the forum"s help of course!

You guys are the bomb!

Hopefully I'll sell it this weekend and get that CE LT4 I have my eye on.

 

Great to hear...thanks.