WC

I live in cold Minnesota so I have kept my six volt battery charged in the tractor all winter.  I put 5w30 oil in it and that seems to help it start, especially if I disengage the rear end with the power lift shifter.  Anyhow, I had a problem with the steering after the restoration I did last summer, so I had to take the mag off to get at the steering u joint.  After putting it all back together and worrying that maybe the mag had gotten off time and checking into all of that, I was able to surprisingly spin it over quite fast with a six volt battery on a rather cold day.  All of a sudden, the starter just quit, dead as a doornail.  I thought maybe I burned the switch out or worse, the starter.  I have not dismantled it because the lights also will not come on which makes me think it might not be the starter.  I put the tester on the battery and I get juice.  I put the tester on the starter and ground on the pto and get juice.  I checked the fuse inside the box on the light switch and it is okay.  What do I do next?  Wayne