Theres a sensor on/near the crank that goes to the computer , then from there it splits off in 2 directions , one for the tach & the other to the regulator in the computer , thats where the alt. regulator is , in the computer , so if you put in the external reg. with out fixing the problem , you may not get the tach to work .
I'm not happy with dodge doing it this way , a pain in the arss for everybody .
So does this mean that your tach wasn't working before ?
As for witch connections to clean / check , it would help to have a wiring diagram , look for all connections at batt. - fusible links , then body & computer grounds , the connector at crank sensor .