Older Ford trucks speedometer/transmission

[Artfuldodger]

For many years, Ford trucks have had a Programmable Speedometer Odometer Module (PSOM) located in the instrument cluster. This module converts the AC voltage produced by the Vehicle Speed Sensor (VSS) to a DC frequency (Hz), which the Powertrain Control Module (PCM) can understand.

 

[Artfuldodger]

My brother has an early 90's model E-350 motor home. First symptom was it started shifting hard, sometimes not shifting at all.
We started researching it and it pointed to the Speedometer computer module.

We were leaning the way of suspecting this module. Later the speedometer and the odometer quit working which definitely pointed us in that direction.

There are a couple of fuses that powers this PSOM that one could check first. One fuse powers the dome light. There was a problem with the light fixture screw grounding it's wire.

If the fuses that power your PSOM are good, you can pretty much suspect you have a bad PSOM if your speedometer and odometer aren't working.

 

[Artfuldodger]

In my brother's motor home the odometer would not even show any numbers(mileage). I went to Pull-A-Part and got one. There is also and company on the internet that will rebuild yours.

Ford used this PSOM on some pickup trucks and the Broncos as well. First thing to check if your truck is shifting bad or the speedometer doesn't work is the two fuses. Make sure it isn't a power to the PSOM problem before changing it out.

It was a pain to get the dash apart and pull the thing. We changed the whole instrument cluster but it's easy to change just the speedometer.
We disconnected the P, N, D, R, etc. gear indicator and reused the original.
It has a cable going down to the gear shift mechanism. I think you may be able to just remove the little cable from the gear indicator as well.

His truck now shifts normal and the speedometer/odometer works too.

There is a bit of info on the internet and some Youtube videos as well.

Here is what the speedster looks like;