Not sure if this is the right place to post if not I'm sorry. I have a 95 2500 5.9 cummins automatic. The overdrive switch does nothing when pressed. The light doesn't go off or occasionally it's already off and won't come on. The overdrive doesn't even kick in. Sometimes when its cold outside the switch works for the first run them if I shut off the truck it starts acting up again. I've not been able to find anything online at all about this issue. It would be great if someone could help me! Thanks
-Caleb Taylor

 

The switch just sends a signal to the PCM, and the PCM turns on the light, and won't engage O/D. Need to find out of the switch is actually sending the signal. Get the service manual for your truck from here. Wiring diagrams are in section 8W. Figure out which wire is supposed to be the signal wire, see if you are getting the signal.