Ive got a 31 couple with good 6v pos ground alternator. When i first cut on the battery cutoff it shows discharge until i start then it will move to maybe 8 on the ammeter. If i cut the lights on they are really dim and the altermator does not kick on to make em bright. The ammeter stay at 0 with the lights on while running but if i cut off it will show discharge. The battery will read 6.7 not running and 7.4 running. It does the same thing with the generator.
31 coupe charging dim light problem?
- Thread starter TraVeler
- Start date
Sounds like a bad ground to me. The original ground connection for the headlights is via the bottom of the headlight bucket to the light bar and then to the frame and back to the battery positive. You can clean away the corrosion under the light bucket on the light bar and the bucket.
As a test, when the car is running and charging, touch a jumper wire to anywhere on the outside of the headlight bucket and to a clean radiator shell spot. If you have a long jumper go all the way to the + positive post on the battery. This info worked for me 60 years ago.
As a test, when the car is running and charging, touch a jumper wire to anywhere on the outside of the headlight bucket and to a clean radiator shell spot. If you have a long jumper go all the way to the + positive post on the battery. This info worked for me 60 years ago.
Last edited:
rotorwrench
Well-known member
The alternator conversions usually don't self excite till the rpm is up a bit. Once it excites and turns on then it should remain on under it's own power till the engine is shut down. The GM 10si alternators originally excited through the generator light warning circuit. This is what the two terminal plug was for. If jumped per alternator installation instructions, one of the pins could be used to initially get the alternator to turn on. Generally, it only had to be jumped once and then it would self excite after that.
Definitely check all battery to frame and alternator structure grounds as well as headlamp attachment. The fender supports are pretty well bolted down to the frame but crust can build up in the headlight ground pathways over time.
If that has no affect then there may be a problem in the 10si internal voltage regulator module. I would be curious what type of headlight bulbs it has, ie plain incandescent types or the halogens or what have you. Modern LEDs are expensive but they use very little current compared to incandescents, Halogens use a lot more current so that's why I wonder.
6-volt positive ground conversion kits for the 10si are available on flea-pay and generally contain all the parts that fail.
Definitely check all battery to frame and alternator structure grounds as well as headlamp attachment. The fender supports are pretty well bolted down to the frame but crust can build up in the headlight ground pathways over time.
If that has no affect then there may be a problem in the 10si internal voltage regulator module. I would be curious what type of headlight bulbs it has, ie plain incandescent types or the halogens or what have you. Modern LEDs are expensive but they use very little current compared to incandescents, Halogens use a lot more current so that's why I wonder.
6-volt positive ground conversion kits for the 10si are available on flea-pay and generally contain all the parts that fail.
Kurt in NJ
Well-known member
The belt can be slipping— take a finger and push on one of the alternator fan blades — if you can push the fan and slip the belt pushing with one finger the alternator can not make full output.
