convert old RM360 to a 3-way with RM2130 parts

The 12V mode would just be for maintaining cold while driving. It draws 10 amps according to the info plate.

We are spending a couple weeks at state parks without AC hookups and some long drives in between parks.

The fridge that does not work makes all sorts of gurgling sounds when AC power is appplied and the coils get hot but there is NO temperature drop inside the box. I think it's dead.

in many cases, the 12v mode, was travel mode, and good only for trying to lessen heat gain

it would not cool a hot fridge, the DC element was less wattage than the AC element, but plenty good for running down the battery IF you made a mistake

besides if you try this
the parts you have to change, are all the control parts, boards everything, maybe even the wiring harnes, as the (2) fridges probably have different wiring

IF you want to swap parts

then i would suggest swapping the old cooling unit into the new fridge
aka then there are no wires or control changes to worry about

It's just an opinion but I agree with BFL. I have a 3 way and twice it has run the battery too low, once when I ran out of LP and once when I forgot to turn the LP on. It automatically switches to 12V with no notification indication.

Yes, I know who's fault it was. Could be mental acuity. Maybe it will never happen as you're alot sharper than me, but...

The point is, if it didn't have the 12V option it would have stopped cooling and the alarm would start telling me the burner was out rather than waiting until the battery was too low to sound the alarm.

Once that happens, it's too low to crank the generator without a jump unless it can be plugged in.

If we didn't hear the alarm, the temperature would have started to increase but I'd rather loose some food than run the battery too low. That's maybe $25 versus $200 for batteries.

I don't know why you would want any 12v mode for your fridge, since that eats so much battery.

Our 1981 camper we got two years ago, had one of those old 3 way Dometics that only worked in AC. The LP had a pilot that worked but it would not go over to main burner from pilot. Result was, we tossed it and went with a new, small, 120v only fridge.

Recently we got a used Dometic 7401L that is also a 3- way but we only want the 2- way. The advantage is the LP on this one does not need a pilot. Plus the freezer and shelving is way better than the old ones.

Perhaps you can get the new fridge working by doing the trouble shooting in its instruction manual?

If not, and you really want the 12v element to work in your old fridge, I suppose you could try to swap them. It would be way better if you could get the new fridge working, and swap the whole fridge.