Dash lights backwards-working suddenly...

I would NOT install an original type IVR. Look up RTE and there is or was a couple / three others

https://www.rt-eng.com/index.php/RTE_limiter.html
Some things you need to do while you have the cluster out

1...provide a ground pigtail to a ground spot on the board (the board mounting screws some of them are ground)

2...Clean and solder jumpers from the springy contacts in the board for the limiter, to the PC board traces

3...Clean the board where the gauge studs go through and make contact. Just tighten/ loosen/ tighten the stud nuts a few times to "scrub" the board

4..Clean the area where the lamp sockets make contact with the board, bend the lamp socket contacts appropriately for better contact, and inspect them for looseness and corrosion. Change the lamps and make certain the socket is clean.

5...Inspect all the PC board harness connecting pins for looseness where they meet the board. clean, flux and solder them at the base, to the board traces.

6 Examine the ammeter for heat damage, as well as the eyelet ends where the big black and big red connect.

Do you have a service manual? If not, run over to MyMopar.com and download one, free. You may have to accept Dodge vs Plymouth, etc etc for some years.