So I wanted to sell my parts truck, the '86 F150 4x4 XLT Lariat. It had been sitting for a couple months. Ran and drove around the farm fine before I parked it. I went to fire it up last night so we could drive it onto the new owner's trailer, seems like a dead battery. No problem, I charge up the battery in the '81 and swap. The truck is still completely electrically dead. No interior lighting, windows, wipers, accessory, start, absolutely nothing. Battery reads 12.4V, same at the battery post on the starter solenoid. Fusible links look good, I get battery voltage on the downstream side of each one.

While I'm standing there with the (now skeptical) buyer, the interior lights flicker and come on along with a relay-type clicking under the dash. We haven't touched anything. Key on, fuel pump cycles and Brake light on (rear circuit is empty). Turn to Start and everything dies again. Back to key off and the lighting comes back, flickers and dies. Comes back a couple times over the next hour or so for ~10sec at most.

To add insult to injury, his trailer ends up being 1ft too short. So despite offering some money off which I agreed with , he couldn't take it anyway. All of this after he drives over an hour to get to my shop.

I know that the hood was left open for one rainfall. I hadn't gone near the truck since before then.

Aside from rechecking the fusible links, where should I look next? It boggles my mind that EVERYTHING is dead, not just ECM or accessories in particular. The fact I can jump the solenoid and she cranks strong, as well as good voltage after all the fusible links, indicates that the connection from battery to solenoid is good.

 

Try using a meter to check for voltage on both sides of the major connectors. I had the same type of problem with my '84 and when we located a connector that seemed to be the center of the go/no-go situation, we pulled it apart and found that one male part inside the connector was completely corroded away. Wired around the connector and everything was back on. Of course it was the main wire in the circuit that corroded. Hope this helps.