Hi All:

Well, I'm massively confused. I've been reading a bunch of past posts and just can't quite seem to put the parts together. Reader's Digest version: '78 280Z, MSD 6A ignition, Holley 4bbl swap (all FI removed). Car runs just fine. Tach don't work. I used the magnetic pick-up trigger for the MSD (green/purple wires to distributor) and not the white wire. I still know which wire used to run from the old coil(?) to the tach (blue wire that runs to the in-line resistor).

Q1) Am I correct in understanding that the tach on a '78 280Z is voltage driven?

Q2) Is the basic problem that there isn't enough voltage from the MSD 6A to drive the coil and the tach?

Q3) Should I use the 8920 tach adapter or the 8910 tach adapter to make the tach work?

Q4) Do you still need the resistor between the tach signal source (MSD or tach adapter) and the tach?

Q4b) If you remove the in-line resistor (2.5k Ohm if I measured correctly), will there be enough voltage to run the tach? Ohm's law and all that...

Q4c) If voltage driven tach, does it happen to be a 1-5V range instrument like a lot of old control system instruments? I say "old" because a lot of instruments are 4-20 mA these days. 1-5V is so 20th century...

Thanks for the help...

You need the MSD 8910 for the tach to work. I have FI on my car and used the white wire instead of the green/purple. You might have to use the white wire.

Chuck