If you have a GM HEI distributor there is a "tach" terminal on it, right next to where the 12v power feed is.

 

It's an Accel aftermarket I presume on a 69 Camaro 350.

 

It's the terminal next to where your battery feed is hooked up and uses the same type connector. It should actually say "TACH" on it and is just connected to the negative side of the coil. An HEI has a coil. It sits on or in the cap, not remotely mounted.

 

Look to see if it has a tach feed terminal. If not, try the (-) side of the coil if it isn't a coil-in-cap style.

 

Will give that a shot when car is back from the shop.

Thanks