Re: 2002 cummins in a 99 dodge ram no tach function
You need to keep the ECM matched to the engine and wiring harness. Swapping pieces will cause random and very unsatisfactory results.
Check a wiring schematic for the '02 and the '99 to track the tach signal wire. Where the harnesses interface may not be getting the correct engine harness wire to the frame harness wire.
Just my 2c worth.
'99 3500 QC all stock, except: BHAF, Southbend Con-OFE clutch. (soon to be fitted with FASS and full gauges, additional "tweaking" as $$ permit)
5 spd, 210K, ORIGINAL VP$$
5.9 engine by Cummins, body by BTC (beat to crap)