Autometer tach calibration


I just bought a Autometer sport comp 5" tach off ebay. The guy sent the directions and they are the right ones, everything hooked up fine except he had cut both the wires to change from 8 to 6 to 4 cyls. The directions describe a blue and orange wire. The tach has blue and brown. Can any one tell me which wires to connect for a 6 cyl.? :confused: