[JP Noonan]

What do you mean it dosen't work? Like it is dead, it bounces, it stops at 1000 RPM? If it doesn't work try grounding the sender input wire (black/purple stripe )the tach should max out then drop to zero, if it drops then spikes then drops it has an internal problem but should still register. Next see if the black/purple is hooked up to the neg side of the coil (the same side as the points). If it still doesn't work hook a jumper wire (a 10' wire with two female termals on its ends) between the coil and the sender input on the back of the tach. Still nada, make sure the tach is getting +12V form the red/white wire, and that the brown ground wire is good. The blk/blue wires are for display lighting.