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Davo, Master technician
Category: Chevy
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Experience:  ASE Master Technician also L1 Advanced Engine Performance Specialist
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1993 Corvette Headlight Problem

Customer Question

I have a 1993 conv corvette with a headligh problem. When the headlight are turned on the motor keeps on working for about 10 seconds (thump thump noise). I replaced the headlight module in the front of driver side motor compartment and it still makes the noise and now the headlights open when the parking lights are selected on the switch. Do you have any suggestions?
Submitted: 10 years ago.
Category: Chevy
Expert:  marc replied 10 years ago.

1. Check the wiring at the headlight door control module. Check for voltage on the Blue/White wire at terminal C with the headlight switch off and 0 volts when the headlight switch is in Park or headlight position.

2. Check the Yellow wire at terminal (A) should have 0 volts with the headlamps switched off and in the Park position. Battery voltage should appear when the headlamp switch is in the headlamp position.

3. Check for a good ground at terminal D.

Customer: replied 10 years ago.
Reply to marc's Post: I should also mentioned that when I plug in the old headlight module the lights open and close in the correct position when selected on the the switch in the car. But the motors keep on making noise. So how do you stop the motors when the headlights are open. As I said it keeps on making this noise for about 10 sec after the headlights are open and closed.
Expert:  marc replied 10 years ago.

Did you check the ground at (D) The test are still the same, The headlight doors recieve power thru the module you have to see why the module is not opening and closing the motor circuit at the proper times.

Still all boils down to terminals A,C or D.

I'm betting on a conection problem in the ground circuit.

Customer: replied 10 years ago.
Reply to marc's Post: I think I may have found a problem with the part I obtained from the dealer. The control module I was given from the GM dealer has a part number 16521297 and the old control module has a part number of 16509737-2. I called the dealer bbut they are closed for the weekend. Do you think that this is the problem?
Expert:  marc replied 10 years ago.

Let me do a little research

Also am checking somthing else out the motor should shut it self off not the module. I am trying to find out what is suposed to stop motor.

Will see what I can find .

Customer: replied 10 years ago.
Relist: No answer yet.
I need to find out what controls the motor to the headlights. I was told that the headlight control module controls the motors. This is why I bought a new headlight module. When I install the new module it will not stop the motors from running and now the headlight open when I select the parking lights. The original headlight module did not do this. I can put back the old headlight module and the lights work proberly but the motors continue to operate for about 10 seconds. The new module does not operate the headlights as the old module. I need to correct the initial problem of why does the headlight motor continue to run after it is closed or opened for 10 seconds. It makes a thump thump noice during this operation.
Expert:  Davo replied 10 years ago.
I tend to agree with Marc.You need to follow the black wire from terminal D it's entire length and check for corrosion or a loose connection.Connections must be taken apart to be checked not just eyeballed.There is a splice indicated inthe wiring diagram.They are famous for corrosion issues.When doing the voltage checks that look for power it should be close to battery voltage not 2 or 3 volts lower.
Customer: replied 10 years ago.
Reply to Davo/diablo666's Post: Hey guys sorry not getting back with you but had to find some more time to work on car. Well I did not find any shorts in the wire; I even ran another wire and made sure it was to ground. This did not work. Yesterday I decided to take apart the headlight actuator and found my problem. The gear in the actuator was worn, not the gear itself but the drive notch on the back of the gear. I was expecting to see the teeth worn but it was the notch in the back of the gear. This explains the thump thump noise. It made a thump noise every time the square drive slipped on the nylon gear on the back side of the gear. As for my headlight module I have an extra module for sale. I will try to take it back to my Chevy dealer. I do not expect to get my $175.00 back. Thanks for your help anyways!

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