I have a 94 2wd automatic cummins, and lately the speedometer and tachometer won't work, and at the same time the trans won't shift higher than 3rd gear, If you know of any solutions, it would be greatly appreciated.

 

Do you have the fuse box also inside the engine bay? If you do i would look to see if you have a fuse or fuseable link burned out.

 

is the alternator charging properly? if not I could be an engine speed sensor issue or a pcm issue. I lost speedo, tach,tc lockup,overdrive and my charging system as a result of a bad pcm but another less expensive culprit is the engine speed sensor.

 

Most likely the speed sensor on the harmonic balancer on the engine. If it cannot read most of pcm functions stop. Clean and adjust stock unit first, then if no results replace. Expect bad parts unless you buy direct from Cummins.

Adjustment is critical.

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Possible if the truck isn't charging and is losing voltage then the voltage regulator might be burned out , you can wire an external regulator in fairly easy, Im sure there is thread on here that tells how to do it if that's what it boils down to