Did you check to make sure that the correct 1142 bulbs are installed? These bulbs are different from a regular single filament bulb in the fact that the base of the bulb has two contacts. Most single filament bulbs have one contact and the metal base is the ground.
The ground for the bulbs comes out of the harness to a terminal that's screwed to the body. The ground terminal should be in the vicinity of the trunk where the fuel fill neck is on the inside. The terminal will have two black wires, one for each B/U light.
If you have an auto trans
the switch is incorporated into the neutral safety switch which is on the side of the trans
where the gear selector lever is located. It needs to be positioned correctly for the switch to work, using a number 43 drill bit (.089" dia.) The procedure is on a recent thread that I have responded to. It's either here on tech or the classic talk section.
On a manual trans
. the switch is located on the shifter itself and the wire color code for either trans
is BLACK/RED STRIPE. The switch interupts the flow of electricity to the bulbs it has no effect on the ground path.