i have a 2000 GS 300 the other day i was stopped with car in gear and brakes applied and the voltage from alt drop to 12.5 volts car almost shut down. i since replaced the alt and the battery with 700 crank amps, replaced serp belt changed battery terminal and still have this problem the ac blows cold even at the low voltage. i also have a after market radio with one amp that is for sub at mono 500w. what could be causing this?

 

How you know the voltage dropped? or did your car just sound like it was gonna bog out? Does it only happen when the brakes are applied? Could have a vacuum leak through your booster. But thats only if it happens when brakes applied.

 

same problem here