first, my car is a 86sport. my alternator voltage is a little low, and when it is tested out of the car the doide pack tests bad. and all my idiot lights are on. now my question is when the idiot lights come on is this because of the diode problem or when the voltage is low. because the voltage it charges at is 13.7 so i didnt think that would be the reason.

also i know i need a new alternator.

 

Lights all coming on means bad alternator. I dunno how it knows, but it's probably from the voltage being low.

New alternators are a gamble. Find a reputable alternator shop and/or save your warranty info. No matter how nice the warranty is the alternator could fail in a matter of weeks (or it could last years).

 

When the alternator is not producing, it outputs a ground signal on the WHITE/BLACK wire on it's small plug. The ground goes to a relay in the CPU. The relay pulls in. The intenal contacts make. Another ground thru the contacts goes to the Warning Light Cluster to cause all the Warning Lights to come on.

See the FSM, Electrical section on how to check out a series four alternator.