64 valiant gauge problems

That insrument cluster is stamped metal. It has small turned back corners that are supposed to hit the dash and complete the chassis ground path. The instrument panel wont function properly while dangling from the harness connectors and may not function properly when mounted in the dash if the ground isn't completed.
Even if the mechanical limter is replaced you would still need a ground path.
The daisy chain of parts and harware is not a conductor when compared to an actual copper wire. A perminant dedicated ground wire is strongly recommended.