Quote:

http://www.forbbodiesonly.com/moparforum/showthread.php?61170-Factory-Tach-with-Electronic-Ignition

There is some confusion in that thread and it stems from the different types of electronic ignitions.
Mopars ignition system using the black box, orange box, chrome box, etc. uses a reluctor to replace point signaling and a large transistor switch to ground the coil to start the spark sequence. As a result, the switching voltages are the same as the old points system so there is no difference in tach signals.
MSD, Mallory and others are what use to be called capacitive discharge systems. They use an inverter to generate around 400 volts to discharge through the coil with a charged capacitor and attaching a tach without the adaptor will destroy the factory tach. IF it did not destroy the tach, it would also be inaccurate as most of them employ multi-spark events on each plug firing at low speeds to insure fuel burn. The adaptor for the tach solves both of those issues.
Craig

2014 Ram 1500 Laramie, 73 Cuda
Previous mopars: 62 Valiant, 65 Fury III, 68 Fury III, 72 Satellite, 74 Satellite, 89 Acclaim, 98 Caravan, 2003 Durango
Only previous Non-Mopar: Schwinn Tornado