Took the truck out for a short drive yesterday, came back home to grab something to take it for a longer one. Shut it off, went inside, came back to start it, nothing. No accessories, lights as if there was no battery at all. Battery is brand new. Disconnected it for a while, starts up like a dream again. After a few starts and off cycles, turn the key, hear a click and then back to square one.
Something else to note. Ever since I test drove it, it sometimes shuts off when pulling over to park - never at a red light though. It doesn't stall, just electrically shuts down but the oil and battery light remain on as in accessory mode.
Now, while it's on and running, i jiggled wires around, positive to and from starter relay (also relatively new), negative (bit of exposed wiring near the terminal), computer wires. Couldn't recreate the issue. The battery terminals are pretty shot and i will be replacing them tomorrow. It all really seems like an intermittently bad ground but I can't be sure. I haven't yet checked what the battery ground looks like at the other end (where does it go?).
Any suggestions would be appreciated.
1985 F-150 XLT Lariat, 5.0 EFI, RWD, 8.8 Axle