We have a old Galion 303 grader with a 6 cylinder IH diesel thats been sitting in the barn for a couple years and we tried to get it started today and it will just barely crank. It will turn over slowly a max of 3 times. The battery is good. We have a huge construction equipment battery on it fully charged and even put the charger on it on fast charge and it still just barely cranks. We tried 3 different batteries that we're all good so that rules that out. I was thinking maybe the contacts in the soleonoid are corroded and aren't transferring enough power to the starter. The battery cables and starter cable are all new. Any suggestions?