1975 Factory CJ Column Mount Tachometer Wiring

[84_CJ7]

I recently acquired a factory column mount tach for my CJ. Can anyone enlighten me on the wiring scheme?
Four wires -
Black
Orange
Red
Red/White

I am guessing black is ground, orange is the distributor, red is power, and red/white is accessory power. Am I right?

Scott

 

[84_CJ7]

After taking the cover of of the tach I discovered that the light is on a separate circuit - orange=light power, black=light ground. So the question is the red, red/white wires.

Scott

 

[XJNick]

One of those two wires will be a switched hot 12 volt source (such as from the ignition switch).

The second wire will be the tachometer pulse signal. This wire comes from the ignition coil and sends "square" wave pulses which the tachometer translates into RPMs. Some ignition coils use a "current" pulse, meaning it is a hot output to the Tach., others use a "voltage" pulse, meaning it is a ground output to the Tach. But, the replacement should be compatible with your ignition coil :mrgreen:

-Nick :!: