Tachometer wiring

[Restomod]

I have a '71 Challenger R/T 340 car with a transplanted 440. The tachometer is not wired to the coil. Under the dash I see three connections to the tach. One has a blue wire with a L shaped boot over it. The other appears to be black with a white stripe and the third is simply a bare bolt. Does this bare terminal simply connect to the negative terminal of the coil? If anyone has a pic of the back of a Ralleye Dash tach, that would be fantastic. Thanks

 

[burdar]

Mines a 73 so things could be different but here is what I have...

This is where the tach wire comes through the firewall. The wire is gray with a black tracer.

Here is the back of the tach. There are only 2 connections. The gray tach wire has a female spade connector and the blue wire has a rubber L.

 

[Restomod]

Thanks, that's exactly the information I was looking for. The ground connection must go through the tachometer body to the instrument cluster. I see how the two wiring posts are insulated from the body with fiber washers.
I am surprised that the gray with bk tracer appears to go through the harness since it gets it's own hole through the firewall. If I can't find the wire through the firewall, I will run another wire from the negative side of the coil to the gray/bk wire and see what I have.

 

[redlinegw]

The male spade terminal on the tach should go to the negative side of the coil and the stud terminal should get a 12 volt switched power. The case is ground. These tachs typically will not work with aftermaket ignition systems like MSD or even Mopar Performance and if they do work they dont work well and are usually very innacurate. Redline Gauge Works can convert your tach to have all new modern internals for around $200 and it will work perfectly. Give Shannon or Andy a call at (661) 259-8891 they can usually turn it around in 1 or 2 days.