A freind has an original tach for a '67-'68 Mustang at a reasonable price. I'd like to buy it, but I'm a bit concerned about getting it to work on my car. I know that factory tachs are not wired like aftermarket tachs, but rather wired in series with the coil. My question is, if I use a Pertronix ignition, can I still use that tach? I don't want to go through the headache of buying a GT harness, since my original harness is in perfect shape, so any advice is appreciated.