On the 93 240 wiring harness I'm installing, the plug for this relay lies below the dash, behind the plastic panel on the left of the transmission tunnel. The plug has four wires, one of which is pink (!). I believe the relay is supposed to be clipped to a support in the area.

Since the power goes through the relay to activate the solenoid that unlocks the shift lever, pulling the relay won't do what you want. You'd then have to override the shift lever lock manually rather than by just pushing the brake pedal.

You might find a way to reconnect the relay leads to keep the solenoid activated whenever the ignition is on. The blue-yellow has power from fuse 12 whenever the ignition is on, and the diagram says the yellow wire leads to the solenoid -- but on my loom that wire is white.

How long will the solenoid last? If I were designing it, I'd take account of the fact that it is supposed to be activated once per trip, and for a few seconds each time. But maybe Volvo picked one that is much better than it has to be.