"Does the field connector have a terminal for the shield?"
Yes it did, and I connected all of those. The powertap battery connection has a terminal for a shield wire so I need to connect that shield wire to battery negative.
"That thing with the switch is concerning. Either the bulb was not rated for 24V, in which case the person you spoke to at Paneltronics gave you bad info, or you've got some kind of crossed connection between then 12V and 24V circuits.
I'm now sure the problem was the bulb. I disassembled the switch, and removed the bulb, reassembled it and all is well, no heat, no little puffs of smoke. The tech desk was positive the switch was rated for 15amps at 24volts, but wasn't sure about the light bulb. The bulb was an odd affair with two wires cast into the bulb and connected to the positive and negative lines. I'm pretty positive I don't have any crossed connections between 12 and 24 volts. Both of the 12V loads are wired directly back to the converters using lines Amel put there for the VHF and something else (maybe the 12V outlet). Before I turned any of the switches on, with the fuse out, I checked them with a volt meter for voltage and polarity. All was well.
The fact that it blew up when you turned it off makes the suspect the latter"
It didn't blow up, just a little puff of smoke, which was plenty for my pucker factor. Interestingly, after switching it on and off several times, the bulb continued to operate, it just got very hot each time.
Thanks for your thoughts,