71-74 Rally Clusters

I have a rally cluster in my '71 RR without a clock or tach. I found one that has a tach that I want to add to mine. I'll also have to use the other gauges in the cluster in mine. I'm questioning if I need any other wiring besides the tach wire to make it work? It will be the only item added, but the other ones will be combined and in a new location, will the current wires be long enough?
Thanks,
Jim

If you have a non tach or clock cluster. You can not just change the gauges over to it. You will need to buy a complete cluster with the tach clock provision.

That's what I'm planning on buying. I just want to know if my current harness hooked up to my current cluster, without a clock or tach, will work with the addition of a tach wire.
Jim

Yep, you just need to add the wiring for the tach.

1 more for good measure. A tack or clock cluster and the wiring will bolt in. The tach wire is separate as stated.