voltage regulator

Buried deep inside the back housing of the generator. GM designed this pile to not be worked on although there are now repair parts available for it. There is no way to test the regulator and you will likely destroy the diode assembly before you get it apart. Also, a lot of trouble is caused by the huge voltage spikes these units develop. It's very common to go through four to six of these in the life of the vehicle. The best way to reduce the repeat failures is to replace the battery at the same time. It will work fine in older cars and trucks, but as they age, they lose their ability to dampen those spikes.