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Guys i am in need of some insight. I have a 1999 24v cummins. This truck has been a headache to say the least but i am at a standing point. This is what has been replaced in the last 6 months and has been at 4 different shops including a chysler dealer. They have all given up but i am not ready too. The truck will only run when the c3 plug on the PCM is unplugged. This is the plug nearest the passenger side fender. This is what has been replaced IP Liftpump- stock replacement PCM- has been flashed to match VIN at chyrsler dealer engine harness has been replaced with one out of a running truck with same year and details( 4x4, auto ) ECM has also been replaced. Injectors were replaced with 100+hp from superior turbo and injection PCM harnes was replaced with one out of a running truck with same year and details I have come up with no codes as i have a CTS2 insight and it says there are none as the other shops have been saying all along. Truck runs great and starts right up when c3 plug is unplugged. You can drive it around and it seems to run good but the voltage, gas gauge, temp, speedo, oil pressure does not read.It also will only shift to second gear and nothing more as im sure its because the c3 is unplugged. I have checked when the c3 plug is in for codes and it comes up with nothing. The gas gauge and Voltage work when c3 is plugged in. I have checked all plugs to make sure they are clean and intact.I have also checked battery cables and all looks good. After going through this forum i also have changed the VSS sensor in the rear end and it didnt change anything. I am looking for anyone who may have any info about this issue and maybe how to diag this to figure out the true problem.