Marker lights don't work.

Found that marker lights will turn on or off when I run over a bump. now to isolate the loose wire.

Traced problem to turn signal/light control. Dust built up between contacts causing failure. Fix action: Remove turn signal/light control unit from vehicle. Remove phillips head screws from underside of steering column housing. remove lower housing. hold up upper housing to allow access to both bronze colored phillips head screws holding turn signal/light control unit to steering column. remove both screws. Remove electrical connection. Remove unit from vehicle. Open the rear cover of the unit to get access to the electrical contacts. The cover is a white rectangle that is held on by raised buttons. Do not unscrew the small phillips head screws. They hold other parts together on the inside. pry the white rectangle off gently using a flat screwdriver. There are 5 electrical contacts. The marker light controls use the middle one. slip a small piece of very fine grit sandpaper in between the contact and sand it clean. The contact arm is springy and can be pulled back a little bit if you need to. When done, check the operation by connecting the wiring to the switch and turning the marker lights off and on. When finished, re-install the turn signal/light control and put the housing back on the steering column.

I had this same problem on my 1994 4WD XE. Illumination, tail and front marker lights did not work. Thanks to the great advice from JWG cleaning the contacts on the light switch control corrected the problem. My appreciation JWG!