Retrofitting a factory tachometer?

I have the gauge with the fuel gauge and speedometer. But I have a manual and would like a tachometer. I have a gauge cluster in a stripped out C10 on my property that has a tachometer. Is it as simple as running a wire from the distributor to the cluster?

Yes. In a matter of speaking. Easiest way is to pull the tach wiring harness from the donor truck as well. Its 3 wires on their own with their own connector.

As said, for the most part, yes. There are other things that will need to be addressed, but if you have a donor cluster it should be "easy".

There's a sticky in the gauge/speedo sub-section that is a compilation of my journey putting a tach cluster in my truck. It's been several years since then, but it should provide some good info for you. I will answer any questions I can to help you along.

https://www.gmsquarebody.com/threads/gauge-cluster-teardown-and-rebuild-beware-pic-heavy.6035/

If you have a donor cluster and its a similar year, the cluster swap is easy. For example, from 73-75 the instrument cluster had a mechanical oil pressure gauge and an ammeter, so using a '74 tach cluster in my '75 was a direct swap. However, later years used an electric oil pressure gauge and a voltmeter, so they would have required some wiring changes.

As already mentioned, the tachometer itself has a separate 3 wire harness, with power, ground and signal. Signal wire connects to the tach terminal on the HEI, power to any ignition-switched power source, and then connect the ground.

Originally the truck may have had a tach filter on the signal wire, but it seems to run fine without it. The fliter is a small silver canister mounted somewhere near the HEI distributor.

Bruce