That would be the computer

 

That is the PCM, AKA glorified voltage regulator.

 

Ya what Oliver said, way better explanation then mine

 

I've got one in my 1991.5. What's it control? Trans has it's own. Strip heaters.

Real question. Should I be grabbing this as a spare? I didn't see the cruise control. Got the fuse box cover/holder, the tps and its bracket, .. transmission computer for $14!!

First pick for my 15 yo son!

M

 

The '91.5 is a special breed of its own.
It has an external VR, so that PCM controls, the wait to start function, grid heater, automatic transmission O/D function and cruise control if the truck has it.
Any other year and/ or engine combo PCM will not interchange with it.

 

I didn't know it was a one year item, but it makes sense. Good information, Oliver!

 

Thanks, but to be clear.
It is not a 1 year only set up, as the '91.0 in a NON intercooled 12V and has NO PCM. The '91.5 is a 6 month only wire harness and PCM and can be very hard to find if you need either.

 

Haha, okay a 6-MONTH item. Yay for having a weird one!

Some years ago, my regulator malfunctioned and it cause the alternator to overcharge the battery and it caused all kinds of problems, including damaging the PCM. NAPA finally found me one but it was faulty. Then they found me another one which worked fine, but what I found interesting is that the shift point into overdrive was different with the replacement PCM than the original.

 

where is the VR on the 91.5 trucks I have never seen what looks like a VR on my 91.5 truck Ken

 

On the firewall.

 

Guess I got to check it and see if it had an external regulator!!

 

The shift points for the transmission are not controlled by the PCM but by the TPS sensor and the setting of the throttle cable and internal hydraulic systems.