tach signal for data logger
 

Installing a data logger and need to source good tach signal ( Racepak). Can I just pigtail off the back of the tach itself? Car is 3.2 motronic mid 80's variety. The signal requirement is 50% duty cycle, 5-18 volt square wave signal ( whatever that means)
Hoping a more technically savy pelicanite could point me in the right direction.
thanks
Willy

Pull the tach out of the dash and (I am 99% sure!) you splice into the black/violet wire which is pin 21 on the DME.

Worked for my LM-1