[Special-Ed]

take both battery connection off and wire brush them

while battery is disconnected... take every ground wire off and wire brush and reconnect
while battery is disconnected... take every accessable possitive cable off wire brush and reconnect,

with battery disconnected, remove all starter solenoid cables... wire brush and reconnect.

with battery disconected... remove the altinator charge wire and wire brush, reconnect.

and then make sure you actually have a ground wire between the motor, the body and the chassis...