You know, re-reading your description and some of the responses, I'm going to say your situation isn't as dire as you might think. You have a lot of stuff working so the visual messy is probably what needs to be chased and remedied. Check a local auto electric shop. As we all know these systems aren't very sophisticated. Having an old car, you need to start accumulating some rudimentary electrical tools, a meter, and a connector assortment. Someone like a Tacoma Screw Products can certainly fix you up but there are others I'm equally sure/ That heater thing as has been stated, isn't electrical. You get hot water from the engine to the heater and the valve is open you should have heat. The valve is open and you don't have heat, the heater core is plugged. How many of you guys have ever seen an absolutely plugged heatercore? Back to this, do you have access to a wiring diagram? Get one, learn the color codes for wiring color get a meter and go snooping. Find out what goes where and don't start cutting wires. Just checking what needs to go where and if it doesn't go there see to it that it does..... Then when you can say everything is hooked up where it needs to be the problems should be lessened one at a time. One case in point is that rear tailight socket that isn't working. Is it corroded? Not all that uncommon on these old pots especially northwest cars. They make stiff wire brushes you can reach into those sockets and wail on the corrosion, then hit it with some dielectric grease and a new bulb and see what you have. If that doesn't work start working your way forward looking for a broken wire somewhere in that circuit. Ignore all the other wires you may be sorting through just the appropriately colored wires going to the socket. That's half the battle when chasing electrical gremlins. Identify which wires may be the culprit for a certain problem and IGNORE the rest. They may turn out to be the culprits as you chase additional problems.