Replacing a KX-170B with a MX-170C
Has anyone done this box for box replacement? Advertising says it is a slip in compatible replacement. I have a concern since the lighting of the display is different. My KX-170B has a display light dimming circuit connected to connector pin 33, as specified by the King Manual. The MX-170C interconnect diagram shows pin 33 dedicated to a VOR Test (?). This is not described in the manual anywhere and there is no definition of what the airplane side connection to pin 33 should be. Maybe it means nothing - I discussed with the mfgr and they could not answer the question.
Also pin 42 is listed as a spare by King, but the MX-170C interconnect shows it is connected to a COM Flip-Flop function - presumable from a wheel mounted push button. (but they do have a note that a resistor has to be added to the computer board). Wonder how that works if you purchase from the likes of Aircraft Spruce?
Thanks for any responses.