The marker lights ground in the housings, you'd have to have a bad ground at each for them to not work due to ground, I THINK, don't know for sure. Since none of them work front or back maybe the headlight switch or the wiring harness/switch connector, that's the part that is common to both front and rear. Juice goes to the headlight switch then on to the lights, the marker lights tee off right at the switch connector, one brown wire going to the front markers and one to the rears. Can't remember any fuses between the switch and the lamps front or rear, and if the headlights work the switch has power. Do the lamps come on when the headlights are on or when the switch is in park lights position or not at all?
