my dad has a 00 sierra with the 5.3 that the alternator just died on. I convinced him to get the 130 amp unit to help with charging the system when we run our trailer winch and for future possible upgrades- as it doesn't have a little extra capability. Anyway, I replaced the alternator and it seemed to charge ok but the voltage jumps around alot and the battery light keeps coming on. We never had any problem like this with the old alternator, and I need to eliminate this issue quickly. I was thinking that it would be the voltage regulator and that we may have to take it off and back for another one... anyone else have any similar issues? The voltage on the guage reads between 12 and 17. I haven't confirmed it for sure with my multi-meter, and the spikes aren't related to rpm's.

 

sounds like a voltage regulator to me....check it at the battery with a meter and if it reads the same then it is out, you can either replace it or get another alternator....