cublex

I have a 74 Cutlass Supreme...last week I had the alternator replace...tonight I noticed the generator light came on when I turn the headlights on and flash when I tun on the signal light...do you thing my battery needs to be replaced?

oldolds88

I think something needs a better ground,or the new alternator has a bad diode

oldcutlass

You need to check voltage at the battery both with the engine running and off. Running should be around 14-14.5, off 12.7ish.

stellar

Why was the alt changed last week? Is the light coming on and flashing bright or dim? Is the belt tight?

cublex

flashing dim

stellar

As mentioned in post #2 check grounds and if they are good check belt tension. If good probably a bad diode bridge or a bad trio. There are a few more possibilities with high resistance in the wiring and the least possible being the battery. The battery may need changed but have it tested. Maybe take the alt back and have it tested or replaced. Still wanting to know why it was replaced in the first place. Was it a used , new or rebuilt alternator you put in? Do you have a volt meter to make some tests?

joe_padavano

Was the replacement alternator a parts store rebuilt unit? If so, I suspect it is bad. These rebuilt alternators have a very high initial failure rate. I just went through this with an AutoZone rebuilt I put in my wife's car. The alternator lasted a week before going bad. Output voltage was fluctuating from 9V to 16V.