Whenever I wanted to defeat the audible alarm on my '79, I would just unplug it, no "jumping" necessary. If there is a jumper wire, that might be the problem.
It is possible that the previous owner rigged 4-way flasher lights. It can be easily done, but if you didn't know about it and something went wrong, it could cause you these problems.
I will find the instructions for those flashers and get back to you.