Option 1 - Pin A - NEGATIVE SIDE OF COIL (non CDI Ignition) With standard inductive ignitions, the negative post on the coil can be used as a RPM Trigger Input Source. If using the Negative Side of the coil as an RPM Trigger Input, use only the Tan/Yel lead provided in Pin A of the tach input connector. This is the only wire used and connects to the negative side of the coil. DO NOT USE THIS SOURCE IF RUNNING A CDI BOX OR ANY TYPE OF IGNITION AMPLIFIER, ECU WILL BE DAMAGED. Option 2 - Pin B - CDI BOX IGNITION Hall type signal input. If using a Capacitive Ignition Box (CDI) or any type of ignition amplifier with a designated hall type tach output signal, remove the Tan/Yel wire and insert only the Wht/Blk wire into Pin B. The Wht/Blk wire is the only wire used; it connects to the Tach Output pin or wire on a CDI Box. NEVER CONNECT PIN B TO THE NEGATIVE SIDE OF COIL WHEN RUNNING A CDI BOX OR ANY AMPLIFIED IGNITION, ECU WILL BE DAMAGED. DO NOT CONNECT TACH PIN ON HEI TO PIN B, ECU WILL BE DAMAGED.

Option 3 - Pin B - DESIGNATED HALL TYPE TACH SIGNAL OR TACH ADAPTERS. The Tach output pin on HEI Distributors and some other ignition systems tach sources are very dirty and cannot provide a clean tach signal to the ECU. In these situations a replacement HEI Module MSD part #83647 or tach adapter with Hall type output signal is recommended. The Hall type Signal output from either of these sources would connect to Pin B on the tach input connector. On MSD distributors this is usually a grey wire and is provided on some Ready to Run distributors also. DO NOT CONNECT TACH PIN ON HEI TO PIN B, ECU WILL BE DAMAGED. Pin C Ground - Pin C is provided for a ground source if necessary for some tach adapters and Mag or Hall type sensors. Do NOT ground to the block. Pin D - Not


that's from the directions... option 3.. they make a big deal about that part in a few places calling it a hall type tach signal...