tachometer not picking up a signal

Hello.The tach on my 260 has never been operational since I have owened it.I picked up a 77 280 to use it as a donor, to keep the 260 on the road.Anyway I replaced 260 tach with the 280 tach, the illumination circuit works and thats it.The wiring diagram in the Haynes manual shows that there is a resistor in line with the blue wire that runs between the tach and the transister unit. I cannot find it on my 280 either.Can't wait until I get me a shop manual,so I can throw this Haynes and Chilton away.I sure would appreciate any input on my problem. Thanks Dale Drummond.

The 280Z tach is not going to work in your point Ign. system, if you just plug it in to the wiring harness. It's wired completely different, and takes it's signal from the negitive side of the coil. the 240 - 260Z tach's had the 12 volts to the positive side of the coil going THROUGH them to get the signal they needed. Your going to need a 240 or 260Z tach.