Gitdyup

I would like to install a Rally Pac. The problem is that I have not found one that will work on my 347 Stroke using a MSD 6AL ignition with the tech output going to a Holly EFI Carb. Note, I have MSD Blaster SS coil. Any suggestions?

99GTvert

Moved to tech forum.

bop11

The tach output is a series of pulses, as long as the EFI and the electronic tach have a high input resistance, and they should have or they would affect the ignition, you can splice a wire into the line going to the EFI. Both EFI and tach just count the pulses but do not effect them. Since you have a mechanical distributor with vacuum and centrifugal advance this should work correctly.

Gitdyup

When I hooked the EFI and the tach to the Tach output wire, they fight for the signal and the car will not stay running. Also, doesn't not have a vacuum advance.

bop11

The old Ford tach are series tachs and goes between the ignition switch and the ballast resistor or wire not directly on the + side of the coil. The pink wire(resistance wire) is needed to make it read correctly which you may have eliminated with the fuel injection.
You need to replace the tach with a modern pulse counter as the old one is a volt meter. It averages the pulses per time into a voltage by means of the inductance in the meter coil. The faster the engine runs the higher the average voltage. This would surely load down the fuel injection system if you put the tach between the plus on the coil to ground.
If you still use the pink wire to feed the coil, you probably could put the tach in as originally installed.