My lil red express started having this problem where when you go to start it the second you turn the key to start it looses all power like someone disconnected the battery and it stays that way for a while until suddenly everything comes back on again by itself until the next time you turn the key to start. When you turn the key power lasts long enough to get a click from the starter relay and that's it.

You can disconnect the battery and reconnect and it doesn't change anything, I've checked for loose connections, tried wiggling wires, replaced the fusible link wire, tried using jumper cables to ground the frame directly and to go from positive to the starter stud on the starter relay where all the positive power goes back to on those trucks to make sure it wasn't some sort of hidden battery cable problem. I've also tried bypassing the amp meter and yesterday I spent more time on it running new wires to completely bypass the bulkhead connector all together and it still does the same thing.
I've gone through the wiring in the bulkhead connectors and all seems good. The last time the power was out I tried disconnecting the starter and alternator to see if something with those was causing it but it didn't help.

Has anyone ever had this problem and know what it was? I'm thinking it might be the ignition switch since that's the only thing that hasn't been touched now but there are some things like the headlights and cab lights that don't look like they go through the switch and they drop out too so I'd hate to spend the time digging into the column to replace it for nothing. Thanks