sspencer,
Use this link, and click on the electrical diagrams for the 73 911.
http://www.pelicanparts.com/914/914_electrical_diagrams.htm
The smoking switch on the stalk certainly seems to be involved but I'm not enough of an expert on electricals to know if the switch is
causing the fuse to blow, or the switch is smoking due to a short that
also blows the fuse.
As far as the garage wiring goes, again, just a guess but it sounds like they rewired the left beam because of a problem in the loom--maybe a bad wire. Perhaps the problem you have now is caused by another bad wire in the loom. Just a guess.
Study the diagrams and I think you may be able to narrow down the problem areas. Also, true electrical experts should add to this thread to steer you to an answer. Whatever you do, I'd definitely inspect the stalk switch as you have major overload symptoms in that area.
Keep us up to date, and good luck.