I have an 1989 E-150 that sits a lot, and the other day it wouldn't start. Just some clicking then total loss of all power. I figured the battery was dead, bit it was fully charged. The inline fuse at the solenoid had blown. It ended up being a bad solenoid and starter, probably from so much sitting. I replaced them, reconnected the battery and it fired right up.
While driving it and sitting at a stop light waiting to turn, all power was lost again. The headlights, turn signal, brake lights, wipers and radio were all on at the time then silence. The inline fuse had blown again. I replaced it, fired it up and drove it home. I parked it and walked away.
Yesterday i tried starting it and got the clicking again and then loss of power again, but no blown fuse this time. I disconnected the battery and looked for other blown fuses but found none. Today I reconnected the battery and it fired right up, so I let it run for a bit headlights, radio, etc on. No blown fuses this time. I shut it off and restarted it with no problem.
We shall see what tomorrow brings. I'm going to start with checking the grounding straps for good connections. Any other suggestions short of it being haunted or just hating me for letting it sit.