Electrical Advice Needed

There are multiple problems with these clusters, you should take the time to pull it out and go through it

In no order:

The PC board connector pins can get loose/ corroded from the PC board traces, you must solder them (or buy a Repop PC board)

The contact fingers for the IVR (gauge limiter) lose contact with the PC board you must solder jumpers across

The IVR itself should be replaced with a solid state one

The gauge studs/ nuts corrode/ get loose. Loosen/ tighten them a few times to scrub the contacts clean

While you are in there, take an erasor and buff clean the copper PC board where the dash lamp sockets go. Bend / clean the socket contacts and clean the sockets and replace the bulbs

Add a ground (I guess you did) to the cluster, but make sure it is actually a ground

This thread has been around a while it is tremendous

Printed circuit pins repair