Hey gang..
Trying to troubleshoot why the tach in my buddy's '71 Challenger isn't working with his MSD tach adaptor. This is what I did to isolate parts of the system:

1. I hooked up the feed from my '70 T/A with standard ignition to the feed terminal on the back of the '71's tach and used the 71's 12v feed on its own tach. I turned the ignition on the '71 and cranked up the T/A, the tach on the '71 worked..

2. I fired up the motor in the '71 and grounded the white wire from the MSD box which is the tach feed and the motor died ( so I am assuming this is what should happen ).

3. I connected the tach feed ( white wire ) from the MSD unit on my Daytona and fired up the Daytona with the ignition on in the '71, the tach didn't work.... mmmm???? The tach works with the MSD tach adaptor in my Daytona.

Is there something different between a '69 B-body tach and a '71 E-body tach? I would think fundamentally, there isn't... Any suggestions?

The four wires of the TACH adaptor are wired properly:
1. white to the tach feed from the MSD unit
2. black to ground
3. violet to feed post of tach
4. red to 12v feed

Cheers,
Troy