Intermittant window cut-out on start

[David_Jennings]

Once again I'm trying to fix my brother's 1989 6.2. Now the problem is with an intermittant electrical shut-off: sometimes when it starts, the windows and other accessories won't work. Sometimes they do. I replaced the ignition switch, the key-lock, and checked the fuses. Nothing. Any suggestions on where we might try next? It never fails to start, but 50% of the time the windows will not work when the engine is running. Other items fail to work as well.
Here is a hint or a guess: the previous owner hooked up fog lights by splicing into a wire. Could that somehow cause the problem? We removed the lamps a long time ago, but the problem with the cut-off is recent. Thanks for any help.

[More Power]

The electrical connectors that pass through the firewall have been known to cause problems. When the situation appears, try wiggling the various connectors while someone is monitoring the dead circuit. That might lead you to the problem source.

Jim