I have a 1983 Honda Magna V45 that only has 5000 miles on it and was last started in like 1992. I am restoring it and have it put back together however there is one problem...

When I try to hookup the battery I plug the positive terminal with no problems obviously, but when I touch the negative terminal there are sparks, I tested the brand new battery at 12.7 volts prior to hooking up and after it sparks and I finally get it connected, I only have about 11 volts and nothing turns on. Before I started taking the bike apart, I hooked up the battery with no sparking and the bike turned over no problem just didn't start. What would cause the negative terminal to spark now when contact is made, and what suggestions do you have for me? This is the last step and it is killing me! Also, after I disconnected the battery, it was warm to the touch. Please help!!