Ben;

Sorry, but I still don't believe that you got a "bad run of lightswitches"...and unless you have an originally Euro delivered or retrofitted high-beam flasher (more below), that function (relay) was never activated for US delivered cars, so if you car didn't have it before, replacing just the light switch isn't going to give it to you afterwards!

I highly recommend AGAINST trying to use the (low current) ground contact of the directional signal momentary switch to supply ground to the horns...it WILL NOT survive this for long (more on this below also).

...do you always dive right in and do vehicular rewiring without consulting and understanding the wiring diagram...no wonder you're blowing fuses (and "exploding" multiple light switches) a 122 electrical system is not the most complicated thing by any means, but it sounds to me like you're moving way too fast for your understanding and possibly abilities. Slow down(!), get a manual, understand, ask here to make sure, then proceed CAREFULLY...and have a few spare fuses on hand!

122 wiring diagram at: http://www.intelab.com/swem/122S%20Wiring%20Diagram.jpg

What's involved in retrofitting the headlight flasher (flash only, or full stalk control of hi/lo beams), as well as improving anemic horns is written up in the Tech Articles section of the SwEm site at: http://www.intelab.com/swem/techarticles.htm
...I do have to say that I am leary of giving you this info...kinda like giving someone silverware with which to eat, and they wind up accidentally slashing their own throat with the knife...

Cheers