Marty, my point is the upgrade kits don't include the mux boards, so you don't have the extra lighting controls. If you move the board from the locomotive to the tender, any extra lighting controls that you had get lost. What you lose is the individual control of the features. On many locomotives, you have separate control of the cab lights, marker lights, and headlight. If you rip the old 5V board from the locomotive and install the standard upgrade kit in the tender, you have one lighting control, the headlight.
One of the benefits of PS/2 electronics was additional controls, but they tend to get lost with the upgrade kits.