I am installing a stewart warner ultra shift light tach in my 00 d r/t connected to the neg side of the coil first start up no problem after the tach flashed it killed the d (quick wire reference to make sure all is correct) connections were secure disconnected the tach and the d starts fine. with the tach connected only a quick start will go then I lose all spark from the coil? wtf did I do wrong??? steve, kensai, mean greenany good ideas???? patiently waiting for a response.

 

well I found the problem (the negative side of the coil spikes voltage any where from 14.3 v to 64.5 volts not a continous spike, intermittent and when the voltage spikes you can hear a slight change in r.p.m. almost a stumble any how that spike caused a malfuntion in the tach that shorted the new tach (the green wire) to cause it to be a constant ground in turn no signal to the coil. remedy to fix installed new tach, new coil, all is working properly now.