Installed in 70 W31. Any way to make:modify Rally tach to work? Engine will not run if connected to - side Flamethrower coil.

 

You may have a short to ground in the tach wiring. In addition the Pertronix III is a multispark system that may cause issues with your tach reading correctly.

 

Your tach requires a square waveform to operate correctly. Call Pertronics and ask if they offer an adapter to put out a square wave.

If not, ask what format their tach signal takes. Then call MSD, who makes electronic tach adapters, and find out if they offer an adapter to get a square wave from the waveform that Pertronics described to you.

In cases where you come up empty, ask whom they would recommend for you to contact to solve the problem.

I know of no way to modify the tach.

 

Are you powering the Pertronix with the factory positive resistor wire? If so, try jumping it straight to battery power, then see if it will run with the tach hooked up. If it does, you need more power. You can use the resistor wire to trip a relay.

 

Put a set of points back in it.
If the tach still doesn't work, the problem is in the tach.
If it works, leave the points in, and toss the Pertronix in the trash can.