So I bought ashift light with a digital tach but I seem to be having a problem wiring it. I wired the green wire to the coil pack on the drivers side closest to the rear (white with red stripe wire). Then I wired the red wire to a power source and the black one to a ground. My problem is that when I start the car the rpm's on the digital tach keep bouncing around between 100 and 300 rpms. I set the shift light and everything but the RPM's are way off and the car is idling just fine. The RPM's dont even follow the car when I rev. Anyone have any idea what the problem could be?

Neal

 

You need a tach adapter.. .I used an Autometer 9117... They have Mustang specific instructions on their website... Gets wired into the backside of the fusebox under the hood and gives a tach signal that will work...

 

So what brand of tach/shift light?

 

+1 http://www.autometer.com/download_instruction/561.pdf