A C D 15

Wide front end, wheels turn to the left. Steering wheel turns freely. Can"t find a reason why it won"t steer. What could be the cause?

Power or manual steering?

Power Steering

Only steering one way is puzzling but here is what I do whenever I pick up a D-Series with PS.
Get it good and hot by driving, cycling the steering wheel back and forth fully repeatedly while driving it.
Drop the fluid, pour some new fluid in as a flush and you will likely see some thick black gunk out the drain hole. After letting it drain a good hour, refill with the recomended ATF from the users manual. Repeat above and make sure you get it good and hot before draining again, leaving it to drain overnight; you should see some crud from the second fluid change as most folks did not service the filler plug atop the bolster, or ran the plug without the copper washer/seal.
Soak the exteded plug/breather in gasoline overnight and be sure to use a pick or wire to clean out the dimples at the plug/breather top at the sides. It is clean when you can add fluid to the bottom of the plug while upside down and the fluid freely runs out all of the dimples under the top of the cap.
Clean it again with brake cleaner as you need to get all the sediment out of the wire mesh inside.
Ever seen a D-Series where the PS fittings don't have small leaks? (buried behind the fram rails where you can't easily get at them to tighten them)
Typically caused by two things; not cleaning the plug breather (the system must breathe), overfilling the bolster, or both.
When you re-fill the bolster, do not fill it as the manual states, just enough fluid to cover the gear 1/4" is sufficient, and keep it at that level.
I have had a number of D-Series that steered hard when purchased and servicing like above has brought every one of them around where I can turn the wheel at high idle very easily, and I have never torn down a pump for rebuild. If washing the tractor, or specifically the radiator, pull the grill and wrap a piece of duct tape around the plug/breather so no water makes it's way into the bolster.