I once had my battery out while all of my lights were on. High beams, dash lights, tail lights. I had to put a good battery in to start it, then move it back to my other car, so I left mine running for the lights. Next thing I know, all the lights were off. The system had burned every light bulb out in my car. Good thing I still had low beams to drive home with. Without a load (battery), the voltage regulator and alternator don't have a reference voltage to keep it down.
Run a long wire around from the alternator post to the starter relay post using a fusible link or 100 amp fuse in series with it. That will bypass your amp guage and the cheap arcing connector at the bulkhead. Use a #10 or larger wire. You may now want to get a voltmeter to replace your amp guage, made by Redline.
Rob