C4 Corvette Headlight Controller Repair

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Introduction: C4 Corvette Headlight Controller Repair

About: Clinical Engineer. PhD, MBA, CET, BMET, MCSE Works with electronic, mechanical, medical, and automotive stuff. Systems Design, Repair, Modification, Repair.

Cars with headlights which "pop-up" are subject to failure of these mechanisms and nomenclature which drives the moving parts. This is the process I used to repair my 1996 Corvette when its headlights stopped working. This is a C4 Corvette, so its dates range from 1983 to about 1996 if I am not mistaken.

The system in a nutshell revolves around a central control module which drives the lights up and down on command from the driver via light the switch in the cockpit. This control module once activated drives the light motors to rotate the lights up and turn on and the opposite when the switch in the cockpit is turned off.

At first this might sound like an electronics nightmare of computers and logic modules, but it really isn't at all. Its basically a matter of manipulating 12 volt lines in the controller to run the lights via a simple logic chip consisting of a series of Op-Amps that latch the command to either up and on or down and off.

this is not about the actual headlights, but about the module itself behind the headlight connection. One module drives both headlights, so it is a common point related to both headlights and is inline with the headlights circuitry. I am not going deeply into the circuitry in and out to the lights, as this is typically not needed as it is a simple circuit, and any designing or engineering has already been done.. this is just to repair the module.

Buying a replacement headlight module runs roughly 200 to 300 dollars, so this simple fix will save you multiple hundreds of dollars obviously.

Step 1: What Makes This Module Go Bad?

First lets look at the big question here...

What makes this module go bad? what is happening?

I have repaired about a dozen of these for friends and fellow Corvette enthusiasts which have basically all had the same issue. What fails is the relay lines fail and burn in two on one of the four lines in them. I can only speculate on what happens, but I think when the light motors age and thus take more power to flip the light assemblies, the burden hits the relay lines and burns the wires in two. I always have seen this affecting only one of the four which operate in pairs.I would suppose something physically holding the lights from moving would also cause this issue as well.

when the module fails, the lights will not raise or lower and require you to manually drive the motors up and down by turning the screws driving them for 10 minutes of turning.. Ugghh. It can be one side or both too. this could be a safety issue if your lights will not raise while you are driving and the night catches you driving.

Her I will show you pictures of what I see and how I resolve the issues I see.

Step 2: Step 1: Identify the Wires and Components

Make sure the car is turned off and nothing is energized without the key in the ignition...

When you pop the hood open, you can easily see the headlights on the front two corners of the car. They are in the down position and are upside down now.

Look for the connectors on each light and you should be able to trace them back to the control module which is located in the driver side headlight well (place where the upside down headlights hides away when off).

The control module has two connectors which are the input and output to the lights. this is the target and needs to come out to examine it.

Step 3: Step 2: Remove the Control Box

The control box is held onto the car with two screws with hex heads. Use your spanner or socket set to remove them.

Unclip the two connectors from the module. they are not the same, so there is no chance to mix them up. they have seals on them, so take care to not damage the weather seals so water can not ingress when connected.

Step 4: Step 3: Take the Box Apart - Look at the Board

The control Box is sealed on the backside with what looks like black sticky caulk. It seals the back panel to the front cover. This must be removed with a screwdriver. I suggest wearing gloves as the black sticky stuff gets everywhere and sticks to everything.

Once you get the plastic box apart, you can pull out the board inside, which is what we are after.

Step 5: Step 4: Examine Board Components & the Relay Data

This board is made of discrete components and none are really static sensitive as they all run on 12 volts. I do suggest taking precautions though as with all electronic components just like they could be damaged... Just in case.

There are a couple of FET power transistors and a hearty logic chip. I took pictures of their part numbers if you need then and your board was char-coaled or you can not see the part numbers.

I also put pictures of the actual four pole relay from Omron. I found these relays on eBay for around $6.00 each and readily available, as were the chips and FETs if you need them.

The Relay is an OMRON MY4-02-GM four line, 12VDC Relay

I have put a picture of the board here as well as the traces on the backside for you to be able to see. I do not have a schematic for the board, but I can make one if I need to.

Almost all the issues I have seen are the big relay in the center of the board. All the other components service this relay to drive the logic of the light system.

Step 6: Step 5: Relay Issues & Checks

The relay is always in contact in either of two states on each line it controls. There are four lines controlled simultaneously.

I take the moving arm loose on the relay so it is only supported by the four connecting wires. This allows you to ohm out the base contacts to the board as well as ohming the contact arms through the wires back to the board.

I have always found one of the wires burnt in two as the cause which is too much current driving through the wire from resistance of the motors or some other obstruction. I see this happen when drive motors go bad, so it might be a good idea to check your headlight motors and associated gears if you do this repair.

You can reconnect the relay wire by soldering it back in place, or replace the relay all together. If you replace the relay, I highly suggest buying a relay socket so you will just have to plug in your new one instead of it being hard-wired to the board as this original one is.

Put it back together and check it out connected to your headlights now.

Step 7: Step 6: Review Board Components & Basic Maintenance

Look over the board and see if any flaws were made putting it together. Bad solder joints is somewhat common, so I suggest redoing all the solder joints while you have easy access to the board. Also clean the contacts of the two connectors using some steel wool to remove any corrosion.

when you put everything back together, be sure to put "bulb grease" in all of the electrical fittings. This seals the physical connections of the pins and sockets to keep them from corroding or growing a gap to cause sparks. I would do this all over your car on all connections if you can.

Step 8: Step 7: All Done! Congratulations!

Now that it is all put back together and everything is working again, you can gloat since you just saved a couple of hundred dollars!! ...and you can drive your Corvette around at night again!

I hope this helps or give you confidence to tackle this job which is not that big a deal.

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    14 Comments

    0
    831mywholeworld
    831mywholeworld

    Question 8 months ago on Step 8

    So my headlights on 85 vette stop going up. Initially I thought it was the motors cause there's no sound. Some back story, during the winter months driving one night went to pull the switch and only the passenger light come out, the driver side was half in half out, so I would just turn it manually, I think snow, and rain got down I'm the relay area and melted the relays, so I cleaned out the black goo and replaced the relays. Took the headlight lamp out an ran a hot wire to them, they work fine, but still won't spin up. I've been looking for the fuse box underneath the dash, still not certain unless it's behind this black box,(see image below) but I found this (image below) is this wire for the headlights

    0
    mrstan
    mrstan

    Answer 5 weeks ago

    I am not sure if you got your lights fixed or not.. I just saw this post where you were looking for fuses and things almost 7 months ago. Let me know if you are still struggling with it. Sorry for the delay.. I have not been on to see anything lately..
    Semnd your pictures if you still want to mrstanskaggs@gmail.com I do not know why they will not post here..

    0
    ChuckH19
    ChuckH19

    6 months ago

    Thank you for an excellent article on the C4 headlight controller module. After taking mine apart I discovered the problem to be one of the two transistors that are riveted to the board. Can you tell me exactly what the specifications are concerning this part? I have seen a few that look correct on a popular auction cite, but there are different voltage ratings on them and none that I saw were 12 volts. Additionally, what causes this failure? I have installed a new motor shortly before the latest failure. The mechanism seems to work very smoothly. I’m thinking maybe a corroded or loose wiring connection???

    0
    mrstan
    mrstan

    Reply 6 months ago

    These are power MOSFETs.. (Ones with three legs). They are called automotive power MOSFETs, and the "ST A531" is the part number to search for. The lower numbers seem to deal with dates or production runs on the ICs. I found a auction site selling a set of these here:

    https://www.ebid.net/us/for-sale/power-mosfet-n-ch...

    They look like they are around $20 paid and shipped. I am trying to find a datasheet to these, but it seems to be elusive. I think they are rated for a high voltage (like 100V) which I believe will compensate the high current that 12V in cars use. I have thought about makings a schematic for the headlight controller board, and maybe it is a good idea such as in this case. With a good schematic, one can extrapolate what values things like these MOSFETs need to operate. I currently do not have a schematic, but I think I will work on forming one for this reason. They work as an automatic switch though as to function in this board. There are two, which parallels the large relay as you have most likely recognized. My assum0ption is that one operates until the other energized to shut off the actuation operation (parallel to three-way light switch in a house). I will know more when I can sit down and actually draw out a working schematic to verify what they are doing. I have included pictures of the actual board and components if you would like to form your own schematic as well. I have tried with dilligence to show the values on all the parts for reference in case one wanted to have a schematic. I will post the schematic here when I get time to form it here. I think it would be benefitial to everyone as well.

    0
    mark.cohen0927
    mark.cohen0927

    Question 1 year ago on Introduction

    I own a 1995 C4. Only the R/H side is giving me "intermittent" problems. At times the light will not rotate up, and at random times for no apparent reason will not go down, causing me to operate the headlight door manually....However, when the car is sitting typically overnight, the headlight will return to functioning normally. This frustrating behavior started
    several weeks ago. Btw 2 years ago I personally replaced the gears with (metal ones), and Delrin bushings on both sides. Do you believe it's the motor that's causing this issue, or would you lean towards the module being defective? Thank you. Kind regards, Mark.

    0
    mrstan
    mrstan

    Answer 1 year ago

    sounds like the relay on the controller board if it seems intermittent. This is kind of thing that happens as the relay ages. Might check the capacitors as well on the board.. they can dry out as they are electrolytic and in an engine compartment to boot..

    1
    jemaruby
    jemaruby

    Question 2 years ago

    Hey! My “F1” wire is burnt. What would you use to replace it? I was thinking about a paper clip. Haha
    Do they sell this stuff? It looks like it’s meant to act as a fuse... I miss Radio Shack!
    Thank you for posting this. It was helpful!

    0
    mrstan
    mrstan

    Answer 2 years ago

    Yes, a paperclip will work just fine as long as you can solder on it.. most paperclips have a chrome layer that is nearly impossible to solder to. A lead from a resister or something will work too. I thought you were talking about the relay at first until I looked at the board picture to see the label F1. It is actually just a jumper as this is a single layer circuit board. It is nothing but a wire from one side of the board to the other side.. just a conductor.

    0
    wdywflife
    wdywflife

    2 years ago

    I have a 96 Collector Edition with all the Grand a Sport goodies. Lately my right headlamp will chatter when turning off the engine. This happens weather I’m running parking lights or full headlamps. No issues with opening or closing its just the chattering once the car is off. Would the module be my issue ? Thanks for your support and stay safe in these uncertain times.

    0
    mrstan
    mrstan

    Reply 2 years ago

    It could be the relay and circuitry on the board in the control module. It could be mechanical too with the bearings in the lights heads if I am understanding your issue correctly. The circuit is based on resistance from the lights once they finish their travel as feedback to the module. I would suggest replacing the main relay and using a socket to do this as well with some bulb grease in the connectors. If the contacts of the relay have carbon'd up, you can see weird stuff happen.

    0
    yikkle1
    yikkle1

    Question 2 years ago

    I'm trying to remove the clear plastic cover inside of the headlight module on my 1992 Corvette without breaking it. Any suggestions?

    0
    mrstan
    mrstan

    Answer 2 years ago

    Are you talking about the relay cover as in the pictures here? There are just two tabs on each side which hold it on. I would use a hook to pop them loose pressing against the circuit board. If you are talking about something beside the relay in these pictures, you might need to send me a picture to know for sure.

    how long have you had this car ??
    I have been looking for this for a long time

    0
    mrstan
    mrstan

    Reply 2 years ago

    I have had this car for 5 years now. It’s been a challenge and educational to be for sure...