The wiring of the switch is the same on both sorts of units, so the difference must lie in different versions of the control board. I don't know offhand if they can be directly interchanged or not. I also don't know that I would care to spend the money for a new control board module to replace a perfectly functioning one.
My generator, similar to yours, doesn't have the prime function either. I've been thinking of installing a SPDT pushbutton on the generator in the fuel pump circuit, with the normally closed contact going to the usual generator control circuitry and the normally open contact to +12V power (and the common to the fuel pump). Pressing the button would operate the pump to prime the system, and releasing it would allow the generator to operate normally as before. This wouldn't make the inside remote switch able to prime; I'd have to go out and open the generator access panel and prime it there. This little project has been on the "to do someday" list for several years, so it obviously isn't a big priority for me.
