In a 240, the OD relay is behind the dash, approximately under the right-center air vent. You get to it by removing the glove box (either 7 or 8 small Phillips screws).

The relay is just through the opening and to the left (toward center dash). It's often "hidden" under a heavy harness and clipped to a metal strut.

Remove and discard the metal clip. The clip can squeeze and distort the plastic housing so badly that it will interfere with proper operation. Without the clip, the relay will remain happily tucked under the harness for the next million miles.

The pictures below show the relay location in my '82. Although the '82 relay (4-spd/OD) is blue and yours is white, the location's the same.