the PS on my TG1860G has come and gone several times since I bought it new in 1998. On one occasion after I replaced the battery, the steering would pull to the left as soon as I started the engine.
The Workshop Service Manual has a procedure on page 5-S20 that remedied the issue for me.
I'll paraphrase it for you...
-jack up the front axle & support it in 2 places such that the front axle can't wobble up or down.
-turn the steering wheel left, then right, then stop at centre (straight ahead).
-find the service connector at the bottom right side of battery looking from front of tractor, at top of electronics module (a square connector with a loop back wire)
-turn ignition key on, do not start.
-unplug the service connector loopback.
-turn off the ignition key.
-re-connect the service connector loopback.
-lower front wheels to the ground, start engine and check for proper PS operation.
hope this works for you.
Pete