[Arran]

On my very similar Northern Electric Bosch clone chassis they used a heavy duty dial cord in much the same way as the bronze cable you used, it looked like it wrapped around the set screw on the hub of the coulored wheel. As to why the set stopped working I don't think it's related to the new cable you added unless the cable is physically stopping the band switch from hitting the detant for each band position. The only thing I can figure is that you may have disturbed something like a grid cap or a component lead about to go, that is unless the set hasn't been overhauled yet.
Regards
Arran