This harness is standalone and is not intended to replace the OEM engine wiring. Standalone harnesses are intended to run the designated engine only, generally when swapped into another vehicle. The first aftermarket harness to facilitate the transplant of a Cummins diesel engine, this harness will fit 2003-2005 5. 9L common rail diesel Cummins engines using standard transmissions. Created with a rugged Bussman weatherproof electrical center at its heart, this harness is ready for the harsh environment of a diesel engine compartment. Integral fuse block circuits include 40 amp relays for fuel pump, fuel heater and ignition circuits. B and ignition circuits are short circuit protected by the 10 mini ATC fuses. Built with pneumatically crimped, gold plated terminals for a positive connection between the PCM and all of the engine sensors. Extra 20 amp fused output wire included to power anything from a CB radio to a ColdShot water methanol injection system. Connectors included for all three styles of accelerator pedal position sensors. Have a bad sensor; find out which one is causing your problem by retrieving diagnostic trouble codes and live engine data through using the OBD2 connector that is wired into the harness. You will notice we don't have a check engine light attached to the OBD2 connector pictured to the right. Chrysler builds their late model trucks with a digitally controlled check engine light. The ECM does not have a driver to turn a light on. Instead, it communicates serially to the instrument cluster control module which controls the check engine light. Got a 2003-4 Cummins and ECM but want to run an aftermarket lift pump; no problem. The 60250 harness gives you a 40 amp relay (pre-mounted and wired into the fuse block) with a 2003-4 fuel pump drive circuit from your ECM. It is as simple as swapping one inline connector to the next. We recommend checking the online manual for the full list of required mating parts prior to ordering.