Electrical problem
1993 Mercury Tracer 4 cyl Front Wheel Drive Automatic 109000 miles

When i bought the 1993 tracer, i had problems running at night. when i used my lights with or without my stereo, and would accelerate, the light would dim and it would drain my battery. i was told it was my alternator, so i replaced that, ran fine for a month or two, then did it again, so i tightened the belts and it ran fine, now another month or so later, it is doing it again. The car runs when i disconnect the battery so my alternator is running, could i have a short somewhere from my battery to my car? i cant figure out whats wrong, again when i accelerate at night it dims my lights, stereo cut outs, n my battery drains, when i park its dead, completely. if u need me to explain more i can, i jus am lost