old tachometer help

[hoiychoiynoiy]

i have an old tachometer from a gmc vehicle, it goes to 5000 rpm, 10 20 30 etc. it has the words "A.C. DIV. G.M.C. flint mich usa" on the back and 3 prongs, one with a red ring on it and 2 unmarked ones, i was wondering which wire is negative, positive, and which is for the ignition coil. im trying to put it on my nissan truck because im too cheap to buy one

 

[txab]

link no worky at this time

[hoiychoiynoiy]

updated origninal post

[&CDFiXER%]

Is that a burnt resistor at the top, next to the potentiometer?

[hoiychoiynoiy]

well that picture isnt my exact tachometer, just the closest i could find on the internet, mine still has the cover on it

[Doug_Scott]

i have an old tachometer from a gmc vehicle, it goes to 5000 rpm, 10 20 30 etc. it has the words "A.C. DIV. G.M.C. flint mich usa" on the back and 3 prongs, one with a red ring on it and 2 unmarked ones, i was wondering which wire is negative, positive, and which is for the ignition coil. im trying to put it on my nissan truck because im too cheap to buy one

 

 

 

My guess would be the red ring one is the positive lead. Try running an ohmmeter across the red and one of the other two, does it have continuity? Now try across the red to the 3rd connector, do you have continuity? If one of unmarked has continuity with the red one, I would guess that unmarked is ground. The other unmarked would be the tach terminal on the coil pack on the top of the hei distributor.

Continuity means any resistance that is not infinit.

 

These are only guesses, but I would use this method if I did not have a wirint diagram for that engine/body.