Help! C4 1990 Headlamp Headlinght Trouble Shooting

[AV8R]

Problem description:
LHS headlamp/headlight assembly won't fully open or close after turning on the headlight switch.

Year/Make/Model/BodyType:
1990 Chev Corvette C4 (white coupe, Southern California its whole life)
84K miles, mostly round town and some freeway trips.

Details:
Ive tried numerous times to turn on and off the headlights where every time the right works perfect and just recently the left side partially opens and doesnt respond there after. I can however open and close the left side manually by turning the headlamp motor knob until it gets to either end of the thread where it stops and the assembly will be either fully up or down. This leads me to think that the gears and bushings are fine, rather the problem must be electrical in nature. Also, with the hood up, I can watch the right side motor's knob spin but not the left side.

What I want to try next:
Later ill get my kid to turn the switch so I can examine the left side closer to see and hear if its making any noises in trying to respond.

Also, I may try switching the left and right side electronic headlamp module (assuming L and RHS are the same, and use separate modules). If this is a good test, then I should be able to see if the problem is with the electronic module or not. If its one module for both, it will require cross wiring jerry-rigging.

I will also see if there is power going to the cable that drives the motor (grey and green I think). I may also try apply power directly to the motor to see if it responds. Will use my battery charger rather than directly to it via battery cables so that the power is limited.

If the problem isnt the electronic module, the motor seems fine, then it will likely be somewhere in the wiring or some thing else upstream from the module. Here Id need more help from others.

Homework and references:
In researching this problem, Ive found some very good links that are helpful, I will list them here for others to follow the breadcrumbs:

Link to C4 electronic module functional schematic:
Headlight clicking and half-turns - repair with pics... - Corvette Forum : DigitalCorvettes.com Corvette Forums
Note: this diagram implies theres one module for both headlamp motors.
If so, it would require a replaced module if either side was faulty.
Id also have to cross wire to test if one side could drive the other.

Headlamp bushing and gear replacement, steps and pictures:
C4 Corvette Headlight Bushing Replacement 1988-1996 | CorvetteMagazine.com

Another step by step with pictures:
Make Your C4 See Well

Where to find the bushings, gears, new or rebuilt headlamp motors:
Corvette Parts and Accessories, Ecklers 1-800-327-4868 - Corvette Parts and Accessories

More resources would be appreciated:
Wiriing Schematics
Pictures of where the module is
Step by step procedures for debug and fixing

other insights in fixing the headlamp problems like mine

Bst Rgds,

Thomas

 

[AV8R]

More field data:
OK, so now Im flip-flopping on what I thought earlier because of new experimentation data. It may be the headlamp motor or the assembly itself needs loosening up.

So when I turn on the lights, the RHS opens up fine and the LHS opens about 2/3 the way before it stops. When I then turn the switch off to close the headlamp assembiles, the RHS closes fine and the LHS sticks and doesnt move.

Note that the LHS motor knob is tight, but I can rotate it CWise to make the assembly move and I can get it to go all the way to close if I want. Then the whole open cycle starts again as described.

I also noted that only turning the LHS motor knob from its stuck and tight state a few turns and its loose. I can then turn the light switch to the off position and both sides close and properly aligned with the body as they should.

This indicates that their is power going to the LHS and its not likely to be electrical, but rather mechanical in nature (unless the current is insufficient or the motor is weak). Something is making the LHS motor bind up early and very tight.

Another piece of the picture is I got my wife to turn the switch on and off while I stood next to the LHS lamp assembly. When the switch is turned on, with just a little hand pressure as the headlamp is coming around to the open position, I can make it open fully. So it seems it takes a little extra help to make it open. But then again, the knob is tight and I have to loosen it a couple turns before it will close again when turned off.

Something is binding up on the open stroke side of the operation.
Does this indicate a bad gear or bushing or something else?

 

[John Robinson]

I have not looked at the LHL on my 93 but about a year ago I was convinced that the nylon bushings were going bad so I disassembled the motor only to find out the nylon bushing in the motor were better than the new ones. Reassembled and still the sticking headlight. I finally found the problem it was the clip for the steel return line to the radiator siphon tank. It was bent out and the corner of the headlight was getting caught on it and not opening. Since you had to remove a lot of things to get to the motor to rebuild it take a close look for any place that you can see a rub or scrape mark on the headlight housing. make sure everything is back exactly were it belongs. Hopefully you will find that the headlight is getting caught on something. Good Luck

 

[94conv.]

Sometimes the brushes in the motor get a little worn and causes that problem, If there is an electrical shop that rebuils pump motors, they may be able to rebuild that for you or clean up the brushes. I actually had the motor for my sport seats cleaned up by our local shop and its back to working for over a year now.

 

[AV8R]

It seems the remedies are somewhere between $50 for 3 bushings and a gear, to $160 (plus $170 core deposit) for a motor rebuild, to $300 for a new motor.

I dont have a lot of time to pull apart a headlamp assembly and rebuild the motor or gear drive, so $160 isnt that unreasonable as long as I send them my assembly for the core charge. Problem is, its a gamble that this is infact the issue.

I didnt see anything hanging up the assembly that might cause the headlamp from locking full open. What continues to seem out of place is that the motor screw drive with the knob on the end is very tight when the headlamp stops 2/3 open. Then its too stuck to pull closed until I unscrew it a few turns out of the tight position. Something is getting the gear stuck at the one end of the travel.

Sounds like either the gear is getting stuck at one end, or the motor is too weak. If I had to guess Id go for the stuck gear. Id rather not gamble with this kind of money.

Any other insights?

 

[English Guy]

If one of the delrin bushes has broken up, could a piece get jammed up in the screw shaft? Taking the unit apart and having a quick look doesn't take long and the problem should stick out like a sore thumb.

 

[AV8R]

How this story ends...

OK so what I ended up doing was this....

I bought a new OEM (not chinese aftermarket) LHS headlamp bracket and motor off Ebay from a Chevrolet repair shop that had an extra set they didnt need or want. Price was reasonable.

Replaced the old with the new and it works perfectly now. Probably was the motor, but I didnt have the time or desire to mess with rebuilding the motor. The repair job took under two hours, because I had to figure out how to adjust everything when using a stock new part that wasnt adjusted for my car. Even had to level the headlamp outer cover so its level with the hood when the lights are off.

I was 95% done and was enjoying looking at my work, then IT happened. A strong wind blew and the hood of my vette came crashing down closed. Fortunately nobody was in the way of it, but I did a bone head thing. I had put the plastic headlamp cover bezel that goes over the back side of the head lamp on top of the windshield where the wiper blades are. Well it got obliterated in to a hundred pieces. :ugh

Back I went to Ebay and bought a new LHS headlamp bezels for 45 bucks and now I have to paint to the original color for a 1990 coupe. Hard lesson learned.

Hey, the lights work perfect though.

 

[boomdriver]

OK so what I ended up doing was this....

I bought a new OEM (not chinese aftermarket) LHS headlamp bracket and motor off Ebay from a Chevrolet repair shop that had an extra set they didnt need or want. Price was reasonable.

Replaced the old with the new and it works perfectly now. Probably was the motor, but I didnt have the time or desire to mess with rebuilding the motor. The repair job took under two hours, because I had to figure out how to adjust everything when using a stock new part that wasnt adjusted for my car. Even had to level the headlamp outer cover so its level with the hood when the lights are off.

I was 95% done and was enjoying looking at my work, then IT happened. A strong wind blew and the hood of my vette came crashing down closed. Fortunately nobody was in the way of it, but I did a bone head thing. I had put the plastic headlamp cover bezel that goes over the back side of the head lamp on top of the windshield where the wiper blades are. Well it got obliterated in to a hundred pieces. :ugh

Back I went to Ebay and bought a new LHS headlamp bezels for 45 bucks and now I have to paint to the original color for a 1990 coupe. Hard lesson learned.

Hey, the lights work perfect though.

Glad you got it working...

have you ever dealt with J&D Corvette in BellFlower ?
They would have the new or exchange/reman units on the shelf.

 

[AV8R]

I know J&D well, as a few others out here. The new old stock part off Ebay was 1/2 the price that I saw from J&D, West Coast, Mid America, Ecklers...

Another project I will have to get around to do, is replace the master brake power cylinder. Apparently, finding these for a C4 is very very hard, and if you find one; its going to be >400 bucks.

Sometimes I wonder if its worth pouring money into these C4s as the price of gas and the cost of upkeep mounts up. But the Vette runs deep in my blood, so I keep paying the bills to drive it.

Then theres my 74 that needs new brakes and carb... does it ever end?

 

[Schrade]

but I didnt have the time or desire to mess with rebuilding the motor.

No one does. We'd rather just swap easy parts and Plug and PRAY repair, and get back to our Droids!

No problem, as long as you're rich!

 

[AV8R]

To loosely borrow and modify a qoute Dr McKoy of the Enterprise...

"Jim, Im a doctor; not an engineer!"

In my case it is:

"CAC, Im an electronics engineer; not a Corvette doctor!"

 

[boomdriver]

To loosely borrow and modify a qoute Dr McKoy of the Enterprise...

"Jim, Im a doctor; not an engineer!"

In my case it is:

"CAC, Im an electronics engineer; not a Corvette doctor!"

Same difference.....!

A good EE would enjoy the additional time spent at work..

You mentioned the brake booster??

I was just shopping those.. not terrible. O'Reilly auto parts has the reman for $115 exchange, thats without mastercylinder. With runs a bit over $300 if I remember right. They should be available at the local pep-boys for a similar price, or whatever parts stores are in your area.

yeah, I've watched J&D go up and up on their prices over the years. Back in 1988 they were completely reasonable and very down to earth. Since they discovered the gold mine in C4 and later Corvette parts, they've gone 'Hollywood'...
I used to go in there the days before the Pomona swap meet and "offer" to take a few things off their hands at 20% off...when the laughter subsided I'd ask who exactly was going to be the guy that had to carry all that stuff to the booth at the swap meet...?
Then I'd remind them that they'll sell it for discount at the meet, so I was actually doing them a heck of a favor buying it now instead of making them haul it out there so I could get it anyway....

I'd get my discount....

If you want to know a salvage guy thats still got both feet on the ground....check with 20th street auto parts in Phx. He's still reasonable and has a pretty fair inventory for this end of the country. They have a website also thats pretty up to date.

 

[AV8R]

Thanks Boomer...

I actually remember the Gary Ave swap meet in Pomona days.
This was before internet and ebay and online stores. I bought a few parts back then for my 74.

Geez, going up and down all those piles aisles looking for gold buried in there somewhere. And all those beautiful vettes lined up.

Remember the rage of having custom pull wagons for parts?

Ah those were NOT the days. Was too dang HOT. But it was more social.

OK... so whats on deck for my Vette owner woes...
1. 90 Vette:
Currently, is at the shop getting all 8 fuel injectors replaced, a bunch of them shorted out and stopped me cold on the road.
If Im lucky, the control module that drives the injectors isnt damaged.
Im told it may have fried my NEW catalytic converter I replace a year ago.
The brake cylinder is leaking slowly because the o-rings are deteriorating.
The ABS light on, which is probably one or more of the wheel sensors clogging up. The ABS pump seems to be strong.
Had to remove and reseal reseat the coupe's hatch back gasket because it was leaking water into the wells.

2. 74 Vette: (my first car, still have her)
Shes a garage queen.
Needs new brake calipers all around. No brake pressure currently.
QuadraJet needs rebuilding
Possibly the motor could use some work, it smokes some. Probably just top end.

As one on a single income and running a young family with kids, this is almost a fight of diminishing returns.
Ill hang on to my 74 as long as possible. Ive always known that old guys regret selling their first car, especially if its a Vette.
The 90 might eventually have to go if it continues to cost alot to keep viable. Shes in beautiful shape otherwise for 80k miles.

I say all this, and Im NOT a car mechanic. Im a mild mannered computer geek!
So is this typical for C3 and C4 owners, or do I have it especially bad?

 

[AV8R]

So the headlamp now works perfectly, and I figured out how to paint the ABS plastic after may failed attempts.
Secret (to a newbie like meself) was to prepare the ABS surface with 400 grit sand paper and then prime it.
Then paint it with the polar white.

Auto parts stores have a GMC white that matches my car very well.





The ABS was fixed after about 1500 dollars...
The pump had to be rebuilt as no new one could be found for it.
Also replaced the ABS module and relays.

Got to love these cars, because they now cost more to fix and own than to sell.

 

[boomdriver]

So the headlamp now works perfectly, and I figured out how to paint the ABS plastic after may failed attempts.
Secret (to a newbie like meself) was to prepare the ABS surface with 400 grit sand paper and then prime it.
Then paint it with the polar white.

Auto parts stores have a GMC white that matches my car very well.


View attachment 4273


The ABS was fixed after about 1500 dollars...
The pump had to be rebuilt as no new one could be found for it.
Also replaced the ABS module and relays.

Got to love these cars, because they now cost more to fix and own than to sell.

I missed the previous post from March...thats quite a laundry list. Similar to mine and everyone elses.

These cars have some unique qualities...they can cast a 'spell' on their owners that forces you to list every slight defect and keep loosing sleep over it until its resolved. Even if somehow the car manages to keep running. You feed it parts (paychecks like an ex-wife) and it gives you another shot at yesterday for a few minutes each time you get in..

1500 has to sting...actually, thats got to hurt ! a LOT...
but, I understand. The early ABS is/was almost bullet proof by design, but when they do fail, you;re screwed. Several yr models right around 87-90 have no compatable parts on other vette models. Other GM models perhaps...but I do not know which. Whenever I see some loose ABS sensors or other pieces, I buy them and just get over the expense knowing that someday they will be worth the trouble..
Glad you got this issue resolved.

 

[AV8R]

Boomer,

What I didnt say about the ABS fiasco, is that the damage to it was caused by rain... lots of rain... and that doesnt happen that often here in So Cal. But last December we had 6 days of hard rain and my 90 vette was outside while I was away. The rain overwhelmed the 20 year old rear hatch gasket, and the water volume filled both rear compartments behind the seats up to the level where the top of the ABS pump is. WHen the rain stopped I check on my car and saw the rain damage and pumped it out with a shop vac. Fortunately, my AAA car insurance covered most of the cost of the ABS damage. Except I was a dork and had upped my deductible from $250 to $500 only months before...sigh. But out of 1500 bucks plus hassle, I ended up paying just the deductible. System is perfect now.

Now theres really only three things wrong with my 90 vette:
1. The NOx failure on the smog test (see other posting)
2. LTPWS light is on after about 3 miles of driving, I think its the common bug this system has.
3. The BOSE Gold CD player errors out.

I just fixed the 4 speaker amplifiers, as I have not had tunes in my car since like 2005. Took lots of pictures on how I did it, not sure if its worth posting here though as I see tons of BOSE postings already on this site. It appears this was not the best quality or designed auto audio system. But it does rock now. Just the CD player doesnt run. Im not sure how to pull the CD/Cassette system out of dash. Im scared ill break the plastic bezel.

The 74 vette (which is my fav) needs basic stuff like brakes and carb and tune. Eventually an engine rebuild. But Ive got kids, so this will be a slow upgrade path. Youre totally on target about how these big boy toys get under your skin (our ego or vainity or whatever) and are touchstone to our ongoing childhood. Look how much we are willing to pay for that.

Cheers