BC96F150

My son has a 96 F150 XLT 4.9L 6cyl. To preface this, the cowl under the windshield has had a serious leak for years that the previous owner tried to fix, but couldn't. The tray is completely rusted through in some areas, and when it rains heavily, the water will run down the inside of the firewall into the cab. We removed the carpet because of the musty smell. I did a quick fix to the rusted through areas with A/C foil tape and some undercoating spray. Apparently I've missed some areas because it still leaks.

Recently, the #18 fuse keeps blowing out. #18 is a 10 Amp fuse that controls the Speedometer and Electronic Shift Module amongst other things, however I only mention those because these are the main issues: The speedometer/odometer don't work and it will not shift up from 1st gear. I do not have a wiring schematic, but I traced the wires to the firewall and ended up unplugging the three harnesses anyway to see if water had got into them. It looks as if it has, so I cleaned them up and ran a fan all night to dry them out.

Because I do not have a wiring schematic my question is if there is something else in that wire loop from the fuse to the transmission/speedometer that could be shorting? A relay or module at the tranny?

Any help is appreciated as the truck is used daily, but is forced to sit right now.

BC96F150

At this point I'm ruling out any water or moisture. Two nights ago I left three main firewall plugs below the brake booster unplugged with a fan blowing on them all night. Then last night, I used electronics cleaner and used compressed air to blow out all the wiring connectors, and again left them overnight with the fan.

This evening I plugged everything back in, installed a fresh 10Amp fuse, connected the battery and turned the key to 'on'. The fuse is fine. Then I start the truck; the digital odometer comes on for a few seconds, then the fuse blows. Yesterday, it would only blow when I put the truck into gear.

Help me understand this please. Fuse #18 description is for:

- Speedometer
- Electronic Shift Control
- Air Bag Module
- Shift Lock
- Day/Night Mirror
- Diesel RPM Control
- Diesel Speed Control
- Overhead Console

Now, the truck only has the items I bolded above. It is not diesel, nor 4x4, nor does it have the day/night mirror nor overhead console. I would imagine that the Shift Lock option is for the 4x4 truck, so that wouldn't apply either.

I am assuming that the Electronic Shift Control applies? Where is this located? How would/could I test it? Please tell me it's not inside the tranny.

I attached a picture of what I believe to be the Manual Lever Position Sensor ... am I right? Could that have somehow gone bad and be shorting out the fuse?

I'm stumped.

BC96F150

It was suggested on another forum that the PSOM may be either faulty or damaged by moisture. This morning I took out the PSOM to visually inspect it, the connections and surrounding area(s). I don't 'see' anything that would be a problem. I know that's kinda tough to do with small soldering connections - 'see' a problem. However, there's no way water got back there so that's out. Something must have just shorted with age or ??? Anyway, below are some pics I just took.

- First is the three firewall plugs just so you know what the hell I'm talking about, LOL!


- Second is the front and back of the PSOM so you too can visually inspect it.



- Third is the dash and plugs which show no sign of water intrusion nor abnormalities.


- Last is the area that first led me to believe it might have been water that started this. I found water on the ledge below that plug where my finger is pointing. When it rains, water will run down the fire wall in a few locations in the cab.


So is there an easy way to 'test' the PSOM while it's out of the dash? Maybe take it to an automotive electronics shop? ... Small electronics shop? Dammit, I just don't want to pay somebody labor when I can do this myself. I have no problem paying for the fix the part itself, or replacement.