I have a 99 dodge cummins 2500. The mirrors first of all, don't have any control over them. But the heated part of the mirrors work. The cab lights that are above the dash work but the one that is above the seats doesn't work. The cargo light doesn't work but I can hear the relay clicking. I checked the IOD fuse and it's good. Please help these small things drive me crazy!

 

Check and see if the mirror control switch came unplugged. My 96 did that far to often, I ended up putting a zip tie around it so it wouldn't happen again.

Does the dome lamp come on with the doors?

 

The connection is not the problem. I checked that, even replaced the switch. The cab lights never works even with the doors but the ones that you can press to turn on work just fine.

 

Download the service manual for your truck from here. Wiring diagrams are in section 8W. Gonna have to do some troubleshooting, to see where the failure is.