you just need to check if he ran the wire from the engine bay driver side fender tach signal wire or he tapped into the blue/white wire behind the engine temp gauge on the cluster. But even if he tapped the one behind the cluster you should be able to solder it back together and it should work fine, but if he tapped the one from the engine just block it off and remove the tach. Even though your cluster now doesnt have a tach, it still has the signal wire.

 

Well I looked today and tried to find where he routed from. I followed the wires as much as I could but lost them under the dash somewhere. So I don't know exactly where they are coming from but I'm going to say it's coming from the engine because the wiring harness behind the cluster looked untapped.