I just got the motor changed in my hot rod. I'm using everything from a 1990 3.9 Dakota 5 speed. This was a running car that I swapped out an older more tired 3.9 for a replacement lower miles 91 3.9. I'm using the 90 wiring that was already functioning for 4 years in this car.
I have a check engine light on that was not on with the other motor. By turning the key on/off 3 times get codes.
12 = battery disconnected recently, OK
31 = Evap system?
32 = Evap system?
36 = ???
41 = ???
and 55 + end of test.

Code 31 & 32? There is no carbon canister on this vehicle, I can bolt on the Evac solenoids,and plug them in, but they won't be serving any function, except maybe turning off the dash light?

Code 36? I have no idea.

Code 41 maybe? The alt doesn't seem to be charging, I swapped it out for another one but it doesn't seem to be working either. (the first one worked before the motor swap I have checked all the wires to make sure I didn't miss anything, and have cleaned all the grounds to bare metal. I have no idea where to look for what.

The car does start and it runs well. Other then the charging system, I can ignore the dash light, if its not something that will cause me grief. Gene

Have you checked the voltage regulator? This might help. http://www.2carpros.com/questions/dodge-...r-on-this-truck