Motorcycle battery electrical problem?

I am restoring a 1983 Honda Magna V45 and when I go to hook up the negative lead on the battery, there are sparks. As a test I connected the positive cable to the battery and connected a 10A ammeter, one side to the motorcycle lead and the other side to the negative terminal on the battery. The reading is well above 10A as the meter flies up to 10A right away. The ignition is turned off obviously I just don't know what the problem is?? I hardly did anything to the electrical system, only disconnected the thermostat, disconnected the two cables on the auxiliary fuel tank, and also the plug on the radiator. As well as unplugged the cable connectors, but those are simple to reconnect (the white plastic plugs that clip in to eachother) I need help desperately because this is the last step until I can try to start it up! Thanks so much in advance!!