How bright should gauge lights be??

I forgot..........what year you working on?

Depending on the year, the cluster may not be well grounded. Run a separate pigtail to a good ground point on the cluster. The PC boards mount in several spots to the metal casting. These must be tight. Run the pigtail to a bolt / nut in, say, your column support

Also, on mine, there were several problems with the board (and the sockets)

The harness connectors were loose or broken. You can repair them. Mine were in bad shape, I soldered pigtails to all the connections on the board traces and used aftermarket "Molex" style connectors

Also, clean the copper where the lamp sockets make contact, and either replace or clean and bend the contacts on the sockets. Inspect them for corrosion inside. "Work" the bulbs in/ out of 'em several times.

You have to remember these girls are getting old

Also, the power comes FROM the dimmer control and TO the instrument fuse. Check for voltage drop there at the fuse clips. They can be rusted, loose, or believe it or not, even the fuse can be defective, that is, resistive. Usually, they eventually blow if that is the case.