We have an old Tach that we used on our old John Deere combine. Would we be able to hook it to a '51 Flathead V-8. It has four wires white, green, red and black. Would someone tell me what each wire does and goes to.

Thanks
Nathan

 

I'd guess they are for +12, ground, lamp, and points. If I'm right, and there is a lamp, you could use an ohmmeter to measure from the lamp contacts and identify two of those wires. There'd be some resistance from ground to the +12 and maybe points wires (and infinite resistance from the "lamp" wire (if the bulb isn't installed). Then try hooking the remaining two wires to +12V one at a time, and tap the other one rapidly to 12V and see which one makes the needle do something appropriate. I wouldn't want to hook the +12 wire to the points because the high voltage on the points might fry something in the tach.

Use at your own risk. Not responsible for damage to tachs or household pets. Void where prohibited. This is not legal advice.

 

Here's a stab at 'er:
Red = + 12 volt
Black = neg grnd
White = illumination + 12 volt
Green = - side of coil (assuming points and neg ground!)

Good Luck!

Todd.

 

If your vehicle is positive ground and the tach is from a negative ground application, it won't work! Should have mentioned this before....sorry.

Todd.

 

also assuming 12 volts