Hello,
So I have a 2009 knightster 1200. I haven't started it in a year because the military left my battery in ga and I can't register 2 motorcycles in germany. I tried starting it with a motorcycle battery and it wouldn't even crank. So I hooked it up to my car battery...the lights come on and when I crank it, it's starts to crank then, all power goes out then a second or two later power comes back on and it's tries to crank for a second then dies. I started looking at the spark plugs and changed them out same thing....wierd thing is when I take the spark plugs out to test for spark they spark...when I try to crank it when then spark plugs are out its continues to crank and does not lose power. It obviously will not turn over or start at that point. Can someone help me with this. Yes I checked the battery terminals and grounds they are all tight .

 

I would start with the easy stuff. Take your battery and have it tested. Sounds like your battery needs to be replaced

 

I already tried to switch the battery and the same results..I'm starting to think it may be the starter, but I'm not sure.