1978 GEN Light on the Dash
Thread Starter
TheCorvetteBen
Joined: Feb 2007
Posts: 4,987
Likes: 144
From: Van Alstyne, TX
1978 GEN Light on the Dash
Working on a 1978 Coupe. The battery is new, and the alternator puts out 14 V when the car is running. GEN light on the dash is intermittent, sometimes is on other times it isn't. Thoughts?
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
Rebuild it or get a rebuilt.
Thread Starter
TheCorvetteBen
Joined: Feb 2007
Posts: 4,987
Likes: 144
From: Van Alstyne, TX
Le Mans Master
Joined: Jan 2001
Posts: 6,741
Likes: 1,383
Acquire the below info and post back:
1. Take a voltage reading at the battery terminals with the car off.
2. Start the car and take a voltage reading at the battery terminals with the car running.
2a. Monitor and document voltage changes if and/or when the voltage changes when the generator light illuminates.
2b. Monitor and document voltage at the alternator terminal output lug.
Report these back and we can start eyeballin' what's going on.
PS- you can get the alternator tested for free at your local Autozone/O'reillys/whatever place. If everything above looks ok, then I would suggest that. My local autozone will even do it on the car...so if you have a local autoparts place nearby, and a fully charged battery, you may want to do this.
1. Take a voltage reading at the battery terminals with the car off.
2. Start the car and take a voltage reading at the battery terminals with the car running.
2a. Monitor and document voltage changes if and/or when the voltage changes when the generator light illuminates.
2b. Monitor and document voltage at the alternator terminal output lug.
Report these back and we can start eyeballin' what's going on.
PS- you can get the alternator tested for free at your local Autozone/O'reillys/whatever place. If everything above looks ok, then I would suggest that. My local autozone will even do it on the car...so if you have a local autoparts place nearby, and a fully charged battery, you may want to do this.
Last edited by carriljc; Dec 3, 2018 at 10:54 PM.
Thread Starter
TheCorvetteBen
Joined: Feb 2007
Posts: 4,987
Likes: 144
From: Van Alstyne, TX
Just to update the thread in case someone searches for it in the future. I installed another alternator (used but good) and the light is out. Funny thing is, the one I removed from the car was a reman unit (bad sign) with a red mark on the bottom (worse sign). The one on the car now is an original GM Alternator and works wonderfully.
