The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 09-04-2024, 03:11 PM   #1
NWSooner
Registered User
 
Join Date: May 2017
Location: Oregon City, OR
Posts: 14
85 GMC C2500 Dash Lights Not Working Please Help

Does anyone have a link to a trouble shooting procedure?

I have no power to the Gray Wire, Green Wire or Fuse.

Thanks in advance......
NWSooner is offline   Reply With Quote
Old 09-04-2024, 04:49 PM   #2
RustyPile
Registered User
 
RustyPile's Avatar
 
Join Date: Dec 2017
Location: Elkhart, Texas
Posts: 1,842
Re: 85 GMC C2500 Dash Lights Not Working Please Help

The dash light power leaves the headlight switch and goes through the rheostat on the front of the switch, then to the green wire.. If the light switch knob is rotated all the way clockwise, this will turn off the dash lights.. Check that first.. If rotating counterclockwise doesn't bring the lights back, the rheostat is probably burned out.. To the best of my knowledge, the rheostat is not serviceable...
RustyPile is offline   Reply With Quote
Old 09-04-2024, 06:43 PM   #3
Dead Parrot
Registered User
 
Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 2,611
Re: 85 GMC C2500 Dash Lights Not Working Please Help

That rheostat can develop dead spots as well. Turn slowly and you might find a live spot.
Dead Parrot is offline   Reply With Quote
Old 09-05-2024, 12:16 AM   #4
NWSooner
Registered User
 
Join Date: May 2017
Location: Oregon City, OR
Posts: 14
Re: 85 GMC C2500 Dash Lights Not Working Please Help

Thanks for the replies, its something else though. I'll keep at it......
NWSooner is offline   Reply With Quote
Old 09-05-2024, 07:25 AM   #5
RustyPile
Registered User
 
RustyPile's Avatar
 
Join Date: Dec 2017
Location: Elkhart, Texas
Posts: 1,842
Re: 85 GMC C2500 Dash Lights Not Working Please Help

Quote:
Originally Posted by NWSooner View Post
Thanks for the replies, its something else though. I'll keep at it......
Wrong assumption... Do you know where that green wire gets its power??? It's from the headlight switch. Actually, it's internally part of the tail light contacts. There is only ONE power source for the switch.. If you have just one light (headlight or taillight) doesn't matter which one) when you pull the knob, you have power to the switch.. The rheostat is on a "branch" of the tail light circuit.. When the tail lights are ON, power is sent to the rheostat.. That voltage moves through the resistor and exits into the green wire.. If you have tail light voltage at the headlight switch, that means power is being sent to the rheostat.. NO power on the green while having power to the taillights means that rheostat is bad..

That's how the circuit works --- no two ways (or "it's something else") about it......
RustyPile is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 08:57 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com