BTL

Hi guys, first post here.

I recently acquired a 1989 F150 Lariat, and it's having some wacky electrical issues. Last weekend I re-wired my boat trailer, and when I was done I plugged it up to the truck to make sure everything worked. Got nothing. No lights, no trailer brakes. That really surprised me so I tested the trailer lights and brakes with a separate 12V battery and sure enough, everything on the trailer worked, so I knew the problem was with the truck.

I started the truck and tested all of the terminals on the trailer coupling (truck side) and got voltage readings all over the place, terminals that should be dead were getting 2-3 volts, hot terminals getting 7-9v. Weird. Later after it got dark, I noticed the dome light in the cab was on. I figured I left a door open, but everything was closed. Nothing could get that light to go off, so I just pulled the fuse. The next day I drove the truck a couple miles and the light on the brake controller stayed on as if I were signaling or braking the whole time. Yesterday I started the truck just to move it and the wipers turned on and wouldn't turn off.

The steering is also hit-or miss. Some days it's very good, some days sloppy and tough to turn. I initially thought that was a mechanical problem but now I'm thinking maybe the power steering pump is flaking out too?

So obviously I have an electrical problem. My question is: where should I start looking? Do you think this is battery related? Starter solenoid? Ignition switch? There are so many things going nuts at once I don't know where to begin!

Thanks in advance for any advice!

Steve83

Start by making sure the truck & trailer are wired to standard. The truck probably is, unless its trailer connector was hacked in by a previous owner. So I'd start inspecting the trailer, and compare it to this diagram:


(phone app link)

Read the caption, too.