On my 1995 Marquis, Cummins 8.2 I have been troubleshooting an inoperative tach. I found that the tach is supplied the signal from the alternator AC. I have the original wiring diagram from Gillig, which shows a wire from ignition to the IGN terminal, the tach to one of the three AC terminals, and a jumper from alternator + to the DUVAC terminal. My coach had the tach wire on the DUVAC terminal and no jumper. Any thoughts before I move ahead to 'correct' the wiring to the original drawing? By the way the alternator has been replaced, and the install was rather shoddy with an incorrect bolt at the top, and dangerously loose output wire that was almost worn through and short to the block. I see no original wire that would have been connected at the DUVAC terminal that would originate at the battery side of the isolator.
Thanks