So me and my brother are building his 98 12v into a welding rig and a few moths ago we dumped about $1000 bucks on new accessories for the motor, KDP, idler pulley, belt tensioner, alternator, AC comp, water pump, thermostat, hoses, belt, gaskets and seals, and also a ATI super damper. when we were done the tach didnt work along with the alternator because the super damper comes out further then the stock balancer so I did some redneck engineering and got the ESS siting in the correct position, and still didn't work. So I bought a new ESS from Cummins and its working now... sort of at least the batteries are charging. The tach is not reading correct and is bouncing all over also the speed will read correct most of the time but sometimes it jumps to 120mph and shuts off and comes back on all other gauges working fine.

here is a video