This close-up shows the diode that is placed between the handle and the positive battery terminal. Power from the solar pack runs down the handle, along the stem of the big thumbscrew and to the diode. A wire from the opposite end of the handle (not shown) is attached directly to the radio's power switch. This photo also shows the socket mount for the oval transistors, though you can actually get a better look at the transistor sockets in the photo below.
Here is another close-up that gives a pretty clear view of the glass diode on the circuit board as well as the transistors and Hoffman IFTs. (Note: the diode used in the P411 series differs from that in the P410 series.)