Like the previous topic grounds can cause big problems. On your frame up front on frame under bumper area you have a ground post check white wires on it for clean and tight connections also check ground wire from chassis battery on frame and batt to make sure they are tight and clean. Muiltible wires on ground post are for HWH jacks and control ckts on fire wall. While your at it make sure battery + connections are good also.
If you don't have the post look for a ground buss or common grounds in a twist splicing nut may have come loose.