With this new information I am pretty sure you opened a rift in the space-time continuum (it sounds like a "zap" as you described) and you are now simply back in time to when the bulb was originally functioning like that. I'm afraid you're now trapped in a loop and will repeat the last few days over and over and over.
That's it. This thread can now wind down.
Well, well, well... Said the man looking at three holes in the ground full of water.
To wire up your aux fan, bear in mind that on old MBs they usually operate on a "switched-ground" principle. The positive is hot, usually only when ignition is on, but the negative to ground lead is switched by either an A/C relay or a temp switch on the engine somewhere. They close and complete a ground circuit to start the fan. Bear in mind that the startup current draw of the fan is higher than its running load, so if you are just touching wires, you very well may feel a zap as some arcing occurs.
Side note: car horns are also typically a switched-negative circuit, vs the "switch" or horn button being on the positive side of the system.
For the headlight, the person who suggested a test lead, logic and systematically tracking it down is on the right track... Poke, prod and trace, and it will sort itself out.