Alternator

[dannmarr]

I was driving my car and everything started to dimm until it stoped running. I had it towed to the garage and the mechanic said the alternator was bad. I had the alternator rebuilt and installed it. After a week of driving it happened again. I brought the alternator back to were it was rebuilt. They claim that it's good and it charges. I checked the plug to the alternator with a volt metter and it's o.k. When I checked the battery with the volt meter the reading was going down as if the alternator wasn't charging at full capacity. I also installed the wire upgrade as instructed in the "how to". A friend mechanic said it is definatley the diodes in the alternator. Any ideas? what should I do? Have it rebuilt again or buy one from subaru? Is there something else I should check?