68-69 factory tach wiring with MSD ignition and Tach Adapter

Orange--dash lamp

Black--ground

Violet--switched 12V

Green--to neg. side of coil

According to this:

http://www.forabodiesonly.com/mopar/showthread.php?p=1969893876

and this

http://www.forabodiesonly.com/mopar/attachment.php?attachmentid=1714601847&d=1363325975

the long stud is 12V, short stud is tach trigger