Free headlight wiring diagram for 1991 gmc sierra k1500

Question edited for clarity.
Question moved to model category.

Jeff is our professional technician, and has given a great rundown of the workings. Here is a physical diagram.

https://www.google.com/search?q=2002+GMC+Sierra+1500HD+headlight+wiring+diagram


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Wiring diagrams.

https://www.google.com/search?q=2001+gmc+2500hd+headlights+wiring+diagram

and

https://www.google.com/search?q=2001+gmc+2500hd+headlights+wiring+pinout

Plus

https://www.alldata.com/diy-us/en

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Ok got a question. Installing a Bluetooth radio in my ‘94 gmc sierra k1500. I have this wire that I disconnect from the tuner part. It the white and dark green wires with the small clips. What is the dark green wire cause there is no spot on the aftermarket plugs for it

Wiring, schematic, electrical diagrams, fuse diag, error codes, torque settings etc are basic contents of these online books they have here on this website www.reliable-store.com I have attached. Must check it out

A bad ignition module can give you fits!!!! Replace it even if it doesnt fix it! You will be glad you did! Most likely that is the problem ,however!

I found my diagrams at outo zone.com

Go to your local auto parts store and look for a book, Haynes Diesel Engine Repair Manual, Part number 10330. It has your wiring diagram and a lot more. I got mine at Canadian Tire.

Check voltage at the circuit box and test the high/low dimmer switch. Corrosion on a ground wire could also be the problem.

check near speed sensor wire is broken in insullator,check continuity to pin point damaged area!

switch burned up due to a short in the tail light wire