tach question
 

How do tachs work. Do they have a positive wire that when it get's grounded that triggers it? The stock tach on my car (77 mustang II) doesn't work with my ignition. I don't think I have been hooking it up right. Well, I just need to know how a tach works in order to figure it out.

Thanks

I just installed a Autometer tach in my 67 and it has 4 wires. Black, Green, White, & Red. White is for the light (just remember white light). Black is ground, Red is hot/positive, and Green goes to the coil. I hope this helps, probably won't though.

Tachs work by reading the amount of pulses coming out of the negative side of the coil. Hook it up as follows: White wire to fuse that dash lights are powered by, black wire to ground, red wire to a constant hot(+)wire, and green wire to negative side of coil. If it does not work properly then see if your ignition has a tach output wire on it and hook the green wire up to that. Hope this helps!