my book says 66 is "field current too high", disconnect power leads at traction motor and check for short circuit in traction motor, and check for short circuit between battery positive and or battery neg at F1 and F2 and battery case.
my memory says this can be caused by a crudy battery and voltage dropping out. pull the battery from the truck and check it then (battery case isolated from the truck).
151 can be related to fuse 5 being blown, and/or the battery being too low to properly charge the capacitors

get the battery checked/fixed and all that acid and corrosion out from the battery box.