Start by having the generator professionally load-tested. In particular, check if all you can get is exactly one third of its rated current output and if "ripple" is high. Those are two signs it has a bad diode. Due to the design, these generators produce huge harmful voltage spikes that destroy the diodes and internal voltage regulator. It is real common to go through four to six replacement generators in the life of the car. To reduce the number of repeat failures, replace the battery at the same time unless it is less than about two years old. As they age they lose their ability to dampen and absorb those spikes.