starters are usely basic, chack batt. volts, 12.8+ is ok and then check with lights on again, 12.2+ is ok. now check batt volts at the batt conn. on the starter. with in .3 of batt. volts? if so ok, now check ground from starter to frame, put one end of the metter on the body of the starter and the other on the frame, have someone try to crank the eng. shold be under about 1volt, if not fix the ground. just for a test try hooking one end of a jumper wire to the eng and the other to the neg. post of the batt. makes for a good ground check. more than likly its something that you did wrong when you did the headers.