Head light dimmer, no brights on the driver's side?

Tiny
SANDMAN427
  • MEMBER
  • 2002 GMC SONOMA
  • 4.1L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 180,000 MILES
When the headlamps are on the low setting, they all work correctly, the headlamps and the daylight driving lights are all on, but when I switch to the bright setting the left high beam lamp doesn’t illuminate and the daylight driving light on the left goes out. I’ve discovered that if I hold the multi-dimmer switch lever halfway all the lights are on and working correctly, but as soon as I let go of the dimmer switch lever and it returns to the resting position the left lights go out. I’ve installed a new headlamp switch, a new dimmer, turn signal, cruise control multi-switch on the steering column, all new headlamps and bulbs, and I’ve checked all the grounds. I used to repair and restore Corvettes for 30 years and I’m a decent mechanic, but I’ve checked everything that goes to the lights. It’s acting as if the dimmer switch is bad, but I’ve replaced it, so as far as I can tell there’s no other switches on the column other than the multi-switch that I’ve already replaced. So, I would really love it if someone could tell me if there’s a switch I don’t know of, or if it’s something else that I’m missing.
Tuesday, March 4th, 2025 AT 11:44 AM

3 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 51,841 POSTS
I assume you checked the fuses for the system as well, (LT HDLP 15 amp under the hood?) This circuit seems to be the one we are having issues with. If the fuse is okay, I would swap out the daytime running light control relay as well, here are the headlight and high beam wiring diagrams so you can see how the system works. Here is the location of the fuse and the relay. Check out the images (below). Please let us know what happens.
Was this
answer
helpful?
Yes
No
Tuesday, March 4th, 2025 AT 2:47 PM
Tiny
SANDMAN427
  • MEMBER
  • 2 POSTS
Thanks for your reply, I’ve checked all the fuses and relays, and I appreciate the wiring schematics, the ones that are in the Chilton and Haynes manuals I have do not match my harness exactly, I’m going to chase the wiring with the ones you sent and hopefully find my problem. Once again thanks for the help and when I get home, (I’m house-sitting for 2 weeks) I’ll keep you updated on what I find.
Was this
answer
helpful?
Yes
No
Friday, March 7th, 2025 AT 11:45 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 51,841 POSTS
Sounds good, I am interested to see what the problem will be.
Was this
answer
helpful?
Yes
No
+1
Saturday, March 8th, 2025 AT 9:32 AM

Please login or register to post a reply.