87 triple e regency converter issue

I would suggest replacing the converter as soon as practical, rather than putting time and money and energy into getting the old one working properly. The new ones will be a significant upgrade from what you have; the DC output is cleaner, the batteries will charge faster and last longer, and a new unit will most likely be more efficient (and hence run cooler). They are not super expensive (a PD9245 is about $160 US from BestConverter, for instance)--not pocket change, but not a vast sum either.

I replaced the Magnatek 940 converter in my class C a couple years ago with the PD unit. You're welcome to the old Magnatek for the cost of shipping (or if you come somewhere near New England and we can meet to hand it off), but frankly I don't think it's worthwhile doing that. It works fine--producing a steady 13.4V output, along with a gentle audible hum.

Sounds like you have a 6300 series converter that is broken. For now, you can isolate the converter part (blue and white wires going to the fuse panel) so it does not over-voltage the batteries. Just use any portable charger to recharge the batteries when you have 120v power. You will still have normal 120v with shore power or gen, and will get your 12v from the battery bank.