This is a stretch - I'm on a witch hunt to complete my APU Jeep.
I'm not 100% sure but my resources suggest the missing electric control box is from either:
General Electric
Jack and Heintz
Valentine Welder & Co.
This is a control box for a DC generator. The generator on my Jeep is a Jack & Heintz G32, however I'm not quite sure which brand control box was used. These were made for the US Navy for starting early jet aircraft and literature is scarce. My guess is the surviving control boxes are from military surplus. If anyone has a lead on one of these, please let me know!
My model Jeep, NA-4 from 1951.
First control box idea, from an earlier 1940's model.
Second, notice how the white gauge lines up with the 1951 photo, and the black gauge isn't seen in the historic photo. And it nearly blends in this modern photo.
My Jeep:
