tachometer installation

[old gm blues]

sometimes I here about stories like this but this is the first time its happenned to me. I just left from an old scrap yard that had a 71 3 ton truck.I asked the guy how much he wanted for the dash gauge assy. (with tach and vacuam gage) as well as the complete heater control assy? He said $10.00 cdn. That comes to about $6.00 US. needless to say its know in my garage.
What I need to know is if anyone has hooked up an oem tach to a pick up coil style distibutor. there there is one wire next to the feed wire on the distributor for the tach and two wires on the tach but I don't want to dammage anything and can it be done??