Disagree at least for now. The main things you need to "fix."
1.. Search out threads on here about the ammeter circuit. There are many Then ask questions.
2....Dana mentioned the pins--the harness connector pins. These are originally riveted/ swedged in place and can work loose. Clean them up, flux with an electronic solder flux (not local store plumbing/ acid) and solder with electronics compatible LEADED solder In my case, several were broken, so I just scraped the traces bear in differnet spots, soldered pigtail wires, similar to the IVR has been done, and used alternative connectors. In my case used Molex style connectors and did away with the originals
3...Gauge studs can corrode and lose contact with the board. Loosen/ tighten the nuts several tmes, and consider replacing the fake nuts with real nuts and maybe star washers.
4...Clean the pc board where the bulb sockets contact, clean or replace the socket bulb contacts and board contact ears, and bend them for better tension
5...The IVR contact fingers can lose contact with the board traces. In the case of a plug-in IVR, solder bridges across from the contact fingers to the board traces, and in your case, make sure the wires for the IVR are flowed with solder with nice joints to the actual board traces