The voltage regulator on my c130 alternator which is stock had to be rebuilt when it failed. I got it back a week ago. I put in back in the car and it started right up. I backed it out of the garage flipped on the head lights... I had my foot on the brake... the windows were fogged up so i rolled the window down an it dropped my voltage down to such a level that it was almost stalling the engine. I let off the window switc and it was fine. did it again after it ran a bit and it didn't change the voltage hardly at all... I go driving down the road and at certain parts the voltage drops and then goes back up. I am not getting any codes... any one have any ideas if that is normal or is something else going on? The battery is about 4 or 5 years old so i am wondering if maybe it is time for my battery to be replaced... not to mention we had an extremely cold winter... i hear cold winters can kill batteries... The car is a TPI 305 1986 Trans Am

 

Could be the battery but it could also be a weak alternator. If you had to rebuild the voltage regulator than the alt is probably nearing the end of it's life as well. Take it to a parts store have them do a load test on everything.

 

sounds like a bad body ground or other ground/fuselink/
batt cable/connection problem-probably would do the
same thing if the heater blower was turned onto high.
Also check the tightness of the pos battery cable where
it connects to the starter.