Instrument cluster fixes/upgrades?

You don't need to add anything for a voltmeter. There is already switched 12V at the cluster--what feeds the IVR for the gauges.



What to do?

There's been about a thousand posts on this subject, so do a search

Check your PC board harness connector pins for loose, and solder the loose pins

Check the contact fingers for the IVR and solder jumpers across to the board traces

Loosen/ tighten the gauge nuts to scrub the PC board / deoxide/ and remake the stud terminals

If you don't have a solid state IVR get one

Clean the PC board traces where the bulb sockets contact with an eraser, clean the socket contacts or replace and replace the bulbs / LEDs

ADD a grounding pigtail to a ground point on the board, and bolt that to the column support/ dash frame