If yours is like mine:
1 Inlet from motor (or dual filters)
2 Outlet to cooler
3 Inlet from cooler
4 Outlet to motor--not to filters!
It would help to know what brand thermostat you have, as it may have a different labeling system than mine--mine is marked I1,I2
O1 and O2.
You should end up with:
motor to
oil filters
oil filters to thermostat
thermostat to cooler
cooler to thermostat
thermostat to motor (Again, NOT to the
oil filters!)