[mr0077]

Art, are you sure you should be running a ballast resistor? I have almost the same setup as yours, SW gages and an MSD setup. Per ERA and MSD instructions, I used no ballast resistor...I also had a problem with erratic tach readings just like you describe. I bought a tach adaptor, hooked it up, made it worse. I went back through my wiring and found out I had the "rong" wires hooked up to the tach. Disconnected the tach adaptor, hooked the tach up per wiring diagram and no problemo since then...anyone want to buy a tach adaptor?
Good luck, let us know how it comes out.