Hey everyone, first time posting here! I'm installing a pro flo 4 into my 66 mustang which uses the rally pac tachometer. The tachometer is wired in series with the ignition switch to the positive side of the coil.

I've been searching and haven't found much info about wiring it up to work with the system other than purchasing the msd tach adapter. From what I've found the tach will not function correctly without the resistance noted in the picture. I've also seen suggestions to try attaching to the negative side of the coil but I'm worried this could also potentially damage the tach.
My question is the orange wire that connects to the positive terminal on the coil. Is it only a 12v triggered by the ecu? Could I save myself the money of purchasing the tach adapter and using my original 12v keyed source for the coil power and "tape off" the pro flo's? Or is the factory style not adequate (voltage wise)? Just trying to potentially save some money and extra wiring.

I've been searching and haven't found much info about wiring it up to work with the system other than purchasing the msd tach adapter. From what I've found the tach will not function correctly without the resistance noted in the picture. I've also seen suggestions to try attaching to the negative side of the coil but I'm worried this could also potentially damage the tach.
My question is the orange wire that connects to the positive terminal on the coil. Is it only a 12v triggered by the ecu? Could I save myself the money of purchasing the tach adapter and using my original 12v keyed source for the coil power and "tape off" the pro flo's? Or is the factory style not adequate (voltage wise)? Just trying to potentially save some money and extra wiring.
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