Erratic gauges

That or a bad connection. Known problems: The instrument cluster harness connector pins get loose, you must solder them to the board traces. Gauge studs/ nuts get corroded, loosen/ tighten the nuts a few times. The IVR can be bad OR THE IVR connector fingers can lose contact with the board traces. Solder them across to the traces

Find yourself some ELECTRONIC (not plumbing) compatible either liquid or paste flux and make certain you are using electronics compatible solder. NON acid flux

Last I knew, SRA was sold on ebay, I don't care for the consistency, but it works. Or a liquid flux "pen." These have a felt tip. Keep them capped / sealed. You can soak the tip in isopropyl if it gets finicky

https://www.sra-solder.com/solderin...nic-grade-solder-paste?product_list_limit=all
Here is one source, just a quick search

https://www.ebay.com/itm/1109369543.../CoMuehfEIWlx/EqhNm1QjBIDG|tkp:Bk9SR_7ksPiCZA