I've read several posts on this forum and a few others. All give give great leads and things to look into, but I haven't found a concise answer

I Purchased a 94 F150 with the 302 and an auto trans (unsure which one) last week. Truck has been well maintained, but the speedometer/ odometer/voltage gauge do not work. The guy I bought it from, had only owned it a few months, he said it quit working on him, he pulled the cluster, and sent it to a speedo repair shop who fixed it, and claimed it was working before I test drove it. He offered to keep the truck and have it sent back before I took possession, but the shop is close to my house, so I said I would take care of it.

I mention this, because I'm inclined to not believe him as fuse #18 was completely missing, but, when I removed the cluster it WAS super clean, The lens looks brand new, the screws were shiny.

I've driven the truck about 50 miles, all without fuse #18 in, I just realized it was missing today, and replaced it. Fuse #8 is intact. dome light works, transmission shifts like a dream.

Unless I'm mistaken, it shouldn't be PSOM because transmission acts fine, accept maybe if have a 4R70W. And also, the voltage gauge

It's not the fuse, because I checked that, replaced it, AND the dome light works.

Its not the VSS because its not just the speedo, but then again, I feel like I saw the O/D flash at me a few times on my test drive, but not since.

Cluster is currently on my kitchen table, so I guess I can take a peek at the PSOM before I drive it to the shop.

Thanks in advance for any advice

 

I took the PSOM out tonight, to my untrained eye, it seems fine. But it's obviously been re-soldered, likely recently. Big shiny globs of non factory solder on about half the board.

Back to the shop tomorrow it will go.


PSOM

 

Yikes. I'm not a fan of those solder joints. Maybe find another PSOM to replace that one, or send it to a different shop to have it repaired correctly.

You can check pin 1 and 3 on your PSOM connector for 12v with the key on, and check pin 2 for ground. If those are reading the correct voltages, then it's definitely your PSOM. Fuse 17 controls all the gauges, lights and the tach. Fuse 18 is PSOM. Does your cruise control work? If it does, than your PSOM is working internally, and sending a signal to the ECU; It's just not moving the needle.

 

Took it back to that shop. Voltage meter was a loose pin and they fixed it.

On their bench, everything worked just fine. Odometer showed up with the right mileage, it rolled over another mile while it was "running". He showed me all the voltages and everything looked perfect.

He said what he sees often is either a bad ABS or airbag module. Or, loose wire on the VSS. Cruise doesn't work, as it won't if the VSS isn't sending signal to the PSOM to maintain.

Now that I think of it.. I locked up the brakes by accident when I bought it, I remember thinking "definitely no ABS". I assumed it wasn't equipped.

 

Alright so heres where I'm at.

I have it all back together, truck runs just fine. Speedo/odometer arent working

As soon as I turn the key to "on" it blows fuse #18. I've been through 3 brand new 10 Amp fuses.

Edit: on another forum, i read to unplug the airbag control module/airbag diagnostic module under the dash, right by the gas pedal.

That fixed it, speedo/odometer are working, no blown fuses.

But now my battery light is on, lol. Can't catch a break.

 

Fuse 18 also supplies power to other circuits/components:

 

this might help.

 

Its the airbag module. Unhooking it, and replacing fuse 18 restored speedo function

 

Seems to be an increasingly common failure these days.