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Clayso, Master Automobile Technician
Category: Chevy
Satisfied Customers: 880
Experience:  ASE Master Certified Automobile Technician. 30 Years Experience.
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Replaced headlight module where 2 wiring harnesses go.

Customer Question

Replaced headlight module where 2 wiring harnesses go. Lights flipped open on demand and closed properly, 15 minutes later they didn't work, and still don't work. did I get a defective module? it worked 1 time after being installed
JA: Just to clarify, what are the exact lights you're talking about?
Customer: headlight on 93 vette
JA: What is the model of your '93 Chevy?
Customer: Corvette c-4
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: adjusting linkage, looking for a limit switch. headlights come on, just won't open
JA: Anything else you think the mechanic should know?
Customer: new module is used. all wiring is working properly and motors are ok
Submitted: 9 months ago.
Category: Chevy
Expert:  Clayso replied 9 months ago.

Hi There, I'm Clayso a certified master automobile technician with 30 years of automotive repair and diagnostic experience.

From your description as long as there is power at all times on the 2 red wires and power with the lights on, on the yellow and white wires and the ground is good, most likely the module is defective. The link below is a circuit diagram for the headlight doors.

Headlight Doors Circuit

Headlight Doors Circuit: Description and Operation

Voltage to open the headlight doors and to power the solid state circuitry is applied to the headlight control module at all times at terminals "B" and "E" of C2 connector. When the headlights are "OFF," voltage to close the headlight doors is applied to terminal "C" of C2. When the headlights are "ON," voltage is applied to terminal "A" of C2 to allow the Headlight Doors to open.

When the headlights are "ON," voltage is applied to the relay coil. The relay contacts close and voltage is applied to the headlight door motor assemblies. ground is provided for the motors through the solid state circuitry until the headlight doors are open.

When the headlights are "OFF," voltage is reversed across the headlight door motors. The motors run in the opposite direction to close the headlight doors. When the doors are closed, the solid state circuitry senses the motors are not operating and ground is removed.

A test light is recommended to assure the circuits integrity. I hope this information is helpful. If you have any questions let me know. You can reply back to me through this thread at any time.

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Expert:  Clayso replied 9 months ago.

I turned this circuit on and changed the diagram to show how the module is controlling the ground to operate the doors.

Headlight Doors Circuit On

Basically the module is supposed to control ground to operate the doors. Think of the relay coil as an electromagnet.

Hope this helps, let me know.