Join Date: Mar 2002
Location: Austin, TX, USA
Get a volt ohm meter or DVM and probe various parts of the fuse panel with the red probe with the black probe grounded. Then turn on various loads (i.e. fan etc.) and see if your getting a drop accross any of the fuses. It's common for the fuse clips to corrode and create a bad connection. You can clean them up, but you might also opt for a replacement harness if you do in fact have corrosion / voltage drops.
You can perform this same test with the meter grounded to the battery post and check for voltage drops along the ground path as loads are cycled. For example, check the engine block, frame, firewall, etc. If you see anything greater than about 1 volt drop (with a heavy load), then seek out the bad ground. Make sure the bonding straps (like on the back of the engine) are in tact. Those often get tossed aside during an engine swap and result in bizarre voltage drop problems or radio static.