Thanks Sixto for the link -- but it did not work for me. Do I need to register and sign in to that site first?

I spent an hour with a multimeter and got some good info and solved the second problem.
There was a 7.6amp draw with no Key. Going through the fuses made #2 look like the culprit. Turns out it is my crappy old aftermarket radio... which had stopped working some time ago. Removed the radio, and now there is no voltage draw with no key -- problem solved.
YEY!
If I got it right, now I no longer need to unplug the battery at night.

Back then to problem #1 -- no horn, no reverse lights. Looking at the fuse box, fuse #14 is Lord over many diverse things!
I know that the heater control valve was malfunctioning at some point, but the no horn problem pre-dates the valve problem. I went ahead and disconnected the valve and my broken antenna.
I am still trying to sort it all out, but I have a good start.

Your input would be very helpful.
THanks!
-Steve

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1984 300TD wagon with heated dual-tank WVO.