d.l.anderson wrote:
....

Would anyone have a source for the tray-locking cam nut on the bottom
of the 459A? Mine's missing; somebody must have unscrewed it all the
way.

I have several defunct 359/259s. Email me and I will mail you one.

First, a disclaimer. You're treading in FAA avionics repairman
territory for a certified unit. 'nuf said.

The RT459A is a 14v unit internally, and is connected to a 28 volt
supply through a dropping resistor on the back of the mounting tray.
...

I am aware of how to operate it on 14V or 28V. However, note 1 on this
reference
http://www.aeroelectric.com/Installa..._459A_859A.pdf
implies that some internal jumpers must be moved in order to change the
illumination for 28 to 14V. Poking around with an ohm meter suggests
that the illumination lamps inside the unit are in a series/parallel
configuration, so the fact that one of the lamps are intrinsically only
5V is not inconsistant...