PS-2 5V to 3 are always a no no even if wired the same. Different battery voltage, different speaker. The other issue is that many RK 5V had board in engine only battery and speaker in tender. PS-2 3V RK board is almost always in the tender along with everything else.
Then you have Mux versus non mux.
MTH wiring convention is actually pretty consistent on 10 pins. Especially for 3V engines, and now PS-3.
Now plug a tender tether in upside down and you immediately destroy the 3V board because AC track voltage put onto the DC circuit of the 3V board in the tender. G