Choose a pin which is capable of handling the current draw required for the Line Pressure Control Solenoid. See the workshop manual to determine the expected current draw. 

All Nexus DPOs are rated for 3 Amps, but some like the HBOs (Half-Bridge Outputs) are rated higher (5 Amps). See the Haltech Nexus QSG or Wiring diagram for more information.

If you are unsure of the current draw, play it safe.