So i've had the 97 F150 4.6l 4x4 with 260k miles on it for a few months now - just a handy ol truck to have around. Everything worked on it up until we had a huge couple days of rain...
Blower fan stopped working...
Flashers work when key is off - but when key is on / truck is running, the dash lights are all out, except both turn signal indicators and the headlights light are always on. Turn signals do not work.
There's a faint buzzing like the door is open all the time.
when I turn off key, all the dash lights come back on and stay on and drain the battery (!)

Now it has not rained for a few days I thought it'd 'dry out' and go back to normal but not so.

Yesterday looked at all the fuses, looked at the multifunction switch, nothing looks amiss anywhere.

So confusing and maddening! Has anyone had any of these problems?

 

A common problem on these models. Likely that windshield leaks allowed moisture into the cab fuse block and GEM (General Electronics Module) which controls the cab electronics.

Inspection is warranted. Videos on removal are available on Youtube. Others describe the task as not complicated but a PIA.

 

There are videos. You can replace it or fix it.


This one gets good at 17:00 -

 

Start by trying to dry out the fusebox/GEM area as quickly as possible (and prevent further water intrusion). A box fan or heater blowing into the area of the modules is your best bet. If you can dry out the water, your odds improve of this not being an event that permanently damages either module. Once water gets in there, it can take a lot of time to get it out.

Oh, and fix the leak and keep the thing covered until you do.

 

Pulled out the GEM

Made in Mexico 04/10/02
module and it looks like a newer version. It has a 2002 manufacture date. I don’t see any water. Everything is dusty and dry as a bone. I don’t see any corrosion. Now I’m even more confused.

 

Looks like a PO had the same problem. If you're fairly well convinced that rain caused the problem then look for other electrical areas that might get wet. Once water gets in to a component it can take a long time to dry out.

I'd start at the underhood fuse box. You didn't say if you drove it in the rain or if it just sat outside getting rained on. Might be a clue about what got wet.

 

If you have inspected the GEM/fuseblock and concluded they are not the source of the problem, then you will need to start checking the fusebox under the hood, as BareBonesXL suggested.

Also, all the related relays and wiring. Perhaps rodents have been chewing on wires or ???? and moisture created havoc.

After the fusebox under the hood, I would start by checking the wires and relays associated with the turn signals and flashers.

In the meantime, as projectSHO89 recommended, dry everything out and keep it covered.

 

Just ran up to the pick a part and grabbed a different fuse block/GEM module going to plug it in and see if anything changes. Also grabbed a turn signal relay but doesn’t explain my issue with the HVAC system and dash lights, etc. here goes nothing.

 

No luck. Same issues with a whole different GEM and fuse block. Ugh.

 

Well, you have eliminated a huge variable and the most common cause of these poltergeist behaviors. Unfortunately, it means you have to keep digging. Study a wiring schematic for interior systems of your pickup. Knowing all the equipment showing failures try to identify a common link. There may or may not be one.

Not knowing the history of this vehicle, if there was a previous owner they may have monkeyed with the electrical. In any case, keep digging, you will find a clue.

 

Check your grounds. You have some things that don't work, and there may be other monitoring devices that pass low current and need a ground to function. Moisture can cause rust expansion. A rusty ground point might be opening up.

Ideally you'd have a wiring diagram and feel comfortable with auto electrical.

p.s. Find the "door open" switch for the overhead light that stays on. Most vehicles have them on the door hinge mounting area but I don't know 97-03. Even though I have one. Older vehicles had constant power to a switch and the switch grounded the circuit to turn on the light. You might have two problems, lack of ground and short to ground.

 

Those went away a long time ago. His truck uses the "door ajar" switches in the latch assembly.

Pull the kick panels and inspect the grounds. Start on the passenger side.

 

Like this ground? Oof

 

Touched

the wire, and it completely fell apart

 

You found a clue ! (And some serious rust issues.....)