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Im not sure this is the right form for a GMC C8500. Maybe some one can steer me in the right direction.
This is a Digger Derick (Telephone pole setter). The truck has a running

light feature while moving . The low beam head lights are not working while running or with the dash switch. High beams work.


Here's what I checked so far.


Checked all the fuses under the hood.
Check the breakers under the dash.
Changed out the head light switch in the dash.
Air brake parking released as it says in the manual. The dash air brake light goes off when released so what ever scenes that is working.
Changed the head lights out also.
There's mention of a running light relay and module on the fuse diagram, but I don't know where they are. If someone could identify the locations that would be my next move.

Thanks from new guy to this form.
 

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Check the relays
 

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Welcome to DieselPlace.
I moved your post over to the "Med. Duty" section

What year is your truck?

:thumb:
 

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There's mention of a running light relay and module on the fuse diagram, but I don't know where they are. If someone could identify the locations that would be my next move.
Wiring diagrams are available at GMUPFITTER.COM and use the search function for the PDF for the Electrical manual to find your lights, fuses, etc.
 

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That was a bust, only one technical bulletin on radios.
I don't think you looked at quite the correct section. Need to be in body builder section, then MD models prior to 2007, then 2002 (or newer years if 2002 doesn't have what you're looking for), then c-series electrical. Try 2003 or 2004 if 2002 doesn't have what you want.
 

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Discussion Starter · #11 ·
Ron,
Unfortunately that didn't work, no info on running light relay or module. Checked 2002 section and early / later sections. Tried Ctrl F keys for a search on relays, went through every one, no mention of running light relays.
 

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Will this help
 

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