Autometer tach wiring?
A quick seach on summit found these Autometer tach instructions.
http://static.summitracing.com/global/images/instructions/atm-4497.pdf
or
http://static.summitracing.com/global/images/instructions/atm-3904.pdf
If you can find the exact one on summit, they should have a link to the instructions listed. Very handy when looking at parts to buy.
Print