Someone please help me before I scrap this P.O.S.!!

I was working on a FiatAllis FR15b loader. Installed a new block heater, cleaned heater core, installed a new mechanical coolant temp. gauge, and a few other misc. things. I went to pull it out the shop and the S.O.B. would not move!! Ran fine when I pulled it in. I did nothing even remotely related to the transmission,other than check the fluid level. I have traced as many wires as possible and they all seem fine. There is a trans. pressure gauge in the dash and it shows plenty of pressure....

Someone please help me before I scrap this P.O.S.!!

Someone please help me before I scrap this P.O.S.!!