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Username Post: 1980 GMC 6 Cylinder Alternator Not Charging Battery        (Topic#368407)
brigdeja 
Poster
Posts: 60

Age: 33
Loc: New York
Reg: 03-03-09
05-12-22 03:06 AM - Post#2841080    

Hey guys. I have a 1980 GMC SIERRA C15 with the 250ci inline 6/3 speed manual. I noticed that the alternator wasn’t charging the battery. What I have done is below, does anyone have thoughts on what to check next? I’m not seeing voltage at the alternator exciter wire and the gen light on the dash cluster is not illuminating.

- Red wire under boot at alternator has battery voltage.
- Red wire in 2 wire plastic plug at alternator has battery voltage.
- No voltage on brown wire in 2 wire plastic plug at alternator.
- Alternator was removed from the truck and tested good at a local alternator rebuild shop.
- Continuity checked good between the brown wire at the alternator plastic plug and the bottom terminal for the “gen light” bulb socket in the gauge cluster. Wires were labeled “Brown 25” on the schematic.
- Continuity checked good between the top terminal for the “gen light” bulb socket in the gauge cluster and the HTR fuse location in the fuse block
- Brown and white wire with a plastic plug found coming out of the under dash main harness. Nothing is plugged into the connector.



 
brigdeja 
Poster
Posts: 60

Age: 33
Loc: New York
Reg: 03-03-09
05-12-22 03:42 AM - Post#2841081    
    In response to brigdeja

Couple things I forgot. I also checked the bulb and socket assembly, there was no continuity across the socket terminals with the bulb installed. The bulb isn’t dark or burned and I don’t see any open connections inside of the bulb either.



 
Tony1963 
Frequent Contributor
Posts: 1286

Loc: Orlando Florida
Reg: 07-09-18
05-12-22 03:48 AM - Post#2841082    
    In response to brigdeja

You cannot always visualize a bad bulb. If the filament breaks, you will not get continuity.

Install a known good bulb and see what happens.



 
brigdeja 
Poster
Posts: 60

Age: 33
Loc: New York
Reg: 03-03-09
05-15-22 06:59 PM - Post#2841240    
    In response to Tony1963

I put a good bulb and socket in, still didn’t work. I found poking around at the back of the cluster that the lights would work sometimes. I pulled the cluster and found contacts were folded over so the bulb sockets weren’t contacting the printed circuit board well. I’m pretty sure the circuit board is bad based on its condition, I ordered a replacement one. Once it comes I’ll try that and see how it goes. Thanks for the help on this.



 
gchemist 
Member #271 Senior Chevytalk Moderator
Posts: 25719
gchemist
Loc: Austin, TX 78748
Reg: 05-09-00
05-16-22 04:04 AM - Post#2841251    
    In response to brigdeja

Nice work. I replaced the circuit board on mine too. Over time, the contacts get corroded. While it's out, you can upgrade to LED bulbs!
Restoration article: http://www.73-87.com/7387garage/interior/g auges_re...

Brighter bulbs: http://www.73-87.com/7387garage/interior/d ashlight...

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles
'08 GMC Acadia 3.6L SLE


 
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