My buddy has a 87 RX7 and he cant seem to keep a charge when tha battery is running. Alternator and battery tested good at 3 different shops. When he starts the car and turns the ac and lights on the voltage reads below 12.. he was told it was the regulator. He was driving last night and all accersories were off but the headlights. He went to stop and got on the brakes and all the lights dimmed. He wants to know your opinions on this..

Thanks

 

Grounds....... check all of the grounding points on the car.

 

There is a single Black wire bolted to the alternator. With a voltmeter place the red lead on this connection and the black lead on the battery negative post (ground) and with the car running and no accesories or lights on the reading should be between 14.1 to 14,7 volts. A reading of less than 12.5 volts means the battery is not being charged.