Here is some info from this site:
http://www.ytmag.com/cgi-bin/store/model_parts.cgi?SearchArea=MF&&md=70&r=zone &pics=1
I was unable to display the site picture of the 3-position spool, but you should see it at the above address when you click to show pictures. I suspect this is a "new" tractor to you, so don't be offended...but the problem may be as simple as changing a switch position. Brakes and differential lock mechanisms should be one-way cylinders, so according to this site info, (if your tractor does not have individual external hydraulic systems), you would need the control spool in the forward position. The picture showed a lever on the spool.
Hydraulic Selector, isolator assembly - For tractors without individual external hydraulic systems. Three-position spool, forward position allows one-way (push) for single acting cylinder. Center position allows operation of the 3-point arms, & the rear position will feed power to a 4-way control valve for two-way (push-pull) operation of double acting cylinder. Fits all MF tractors where 182373M1 lift cover is used. Replace MF cover plate, adds 2 ports I\O ports 3\8: NPT. (Part No: TS300) $94.12 [Enlarge Picture]
Hydraulic Valve Manifold - This 3 Spool Valve Allows Operator To Use Aux. Hydraulics at the same Time Without Valve Switching. Some Tractors may need slight modification on seat.Includes 2 elbows. Models from 1960 and later years. (Part No: 19833A92) $627.00 [Enlarge Picture]
Selector Valve, 3 Way - NIS - A&I Replaces cover plate 180908M1, adds 2 ports. Services lift arms plus 2 external ports with return going back to valve, ports can only be used 1 at a time, 3\8 NPT ports. (Part No: 47S731) $94.58 [Enlarge Picture]
Valve - Valve for TS3200M. Single spool, 4-way, 3-position, spring loaded to neutral. No relief valve, no power beyond option. In & out ports 3\4", work ports 1\2" NPT. (Part No: TS200BA) $163.60 [Enlarge Picture]