Shelby Tach Help

[Mustangmac70]

I need some Tach help. I recently got a new to me 9k Shelby tach that I want to put in my 1970 Mustang. According to the seller the tach was never used and the wires are still to length and in great shape. The tach has 4 wires: red, black, green, and white/red or pink.

The red wire should go to a switch that is live when the key is turned to the on position. I found two fuses in the fuse box so I used a fuse tap to connect the red wire. Between the fuse tap and the main wire I put an Inline Fuse Holder with 5A ATM Fuse to protect the tach. I saw this came recommended from one of the big tach companies.

The black wire I grounded to a piece of metal under the dash.

The green wire I ran through the firewall and connected to the distributor side of the coil.

The white wire has not been connected yet, but I think it is for the light.

As soon as I turn the key the tach goes all the way to redline and when the engine is running it just stays there. As soon as I turn the car off and remove the key the tach drops to zero.

Do you know if I did something wrong or maybe the tach is broken and needs to be rebuilt?

Thank you for any help you can offer. I greatly appreciate it.

[Bob Gaines]

The 4 wire 9K tach's are the reproduction . Check with Branda for the repro schematics.