Tach wire on instrument cluster?

[Taylor]

Alright my tach stopped working and the issue is in the cluster itself, i have an old mini tach laying around and was curious what wire i would be able to use from the back of the tach for the RPM signal to the new unit? Or do i have to run it right to the coil? please let me know

thanks guys

[NAJ]

Before giving up on the Factory Tach try Reflowing the Solder Joints on the Cluster.

[raccoon]

I believe its gray with a blue trace