hey guys, ive had this problem since i got my car 3 years ago and i'm wondering what is causing it...whenever i hit the brakes on my car (even with the headlights off) i go from like 13v to 10v then with the lights on its like to 8.5v...anyone have any ideas? one kid at my job said that its because i still have the original spark plug wires on it, which is true, i do lol....please help? my sound system is dying because of it lol
thanks
-brian

 

You'll have to get some voltages measured with a digital multimeter. Measure it on the battery itself, and also in the cig. lighter (or fuse box). If there is a volt or more drop (difference) there, then you'll have to inspect the two red wires going from the starter, through the C100 bulkhead connector in the firewall, and into the dash.
You haven't mentioned what car it is btw..

 

oh true, youre right, i havent mentioned it lol, its an 87 t/a, i just put in a new alternator and a new battery, the alt is new as of spring and the battery is new as of like less than a month ago...thanks for your help!