I always tap the radr detector power wire to an ignition switched 12v source, this way the detector turns on when you start the truck, and off when you shut it off. The power window circuit is a good place for this, but there are other's you may use as well. (I used the power window circuit on mine because my '87 has manual cranks...but the slot in the fuse box has ignition switched power). The ground wire from the detector can be attached to any of the metal framing in the dash, you should be able to find an existing ground connection and install it there.
-SM
-SM