1997 F-150 with under 50k miles

I did a search and saw some threads about this issue but I think I can shed some more light.
Also, need some expert diagnostics to put the last nail in the coffin of this irritating problem.
Sorry for long post, but I think the details help follow the problem path. Here goes.

It started years ago with the door lock acting up. It would actuate randomly where it could lock you out, or if left undriven long enough, drain the battery.

Took it to dealer and some indy’s. Couldn’t really pinpoint the problem. Took out the door lock fuse.

Time moves on and some other systems start acting up:

- Windows

- Dome/reading light

- Wipers

It seems to act up more often in wet/rainy weather. Not good when wipers don’t work

Took it in again and the suggested fix is a new computer.

Did some YouTube sleuthing and found a guy with the exact problem. Turns out there is a pinch weld where the sealant fails…right above the computer, which also happens to be attached to the fuse box. He finds that the computer is well sealed and therefore dry. The fuse box on the other hand is an assembly of 3 or 4 layers of flat bars carrying current, alternating with insulation sheets. Water gets inside here and has the perfect environment for wicking around and causing all kinds of shorts.

He goes through the somewhat tedious process of disassembly, drying, and reassembly. He also fixes the failing sealant.

Viola, everything now works!!

Looking around my footwell fuse box, I see lightly rusted metal parts – sure signs of moisture having been in the area.

I decided to wait for the rainy season to end and see if the scorching summer would do all of the work for me. After cooking for a couple months, everything works again! I sealed the problem weld, put the door lock fuse back in, turned the key to “on” (so the windows would operate), and all tests good!

But wait, I hadn’t driven it yet. Turns out everything works with he key in the “on” position but engine off. However, when I start it up, SOME things work and some don’t.


So, key “on”, engine not running: Everything works


Key “on”, engine running:

Locks and wipers – YES.

Windows and dome light – NO.

Turn the engine off, key back to on position, everything works again.

So, what changes when the key is “on” and engine running vs key “on” and engine not running?? And it only affects 2 of the formerly problematic systems??

Residual corrosion/shorts in fuse box assembly? Corroded module plugs? But then why does everything work perfectly with key on, engine off?

Something wrong with the ignition switch assembly?

I have checked/tested all fuses and relays. Nothing irregular on OBD scan.

I’m stumped…(but at least the wipers now work when I’m driving). Short of any other solution, I may follow the video below and rehab the fusebox.

Here's the video that enlightened me

 

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