1994 Dodge Spirit marker and tail lights

Check all your fuses. The fuse box cover or lid will give you directions as to which fuse supplies power, through the light switch to the marker and tail lights. Normally these lights are on the same circuit (fuse) as they would be desired at the same time. As well, the brake and turn signals will usually be on a different circuit (fuse) from the tail and marker lights.

we have already checked all the fuses, but thanks for the suggestion... where would you go next?

O.K., you checked the fuses, I assume that means that each fuse has power on both sides? A fuse can be good but not recieving power. Let us say that the fuse has power (coming in and out). These fuses are non-swithced, meaning they should have power even with the key off. That is why turning off the car doesn't turn off the tail lights. Power for the marker and tail lights leaves the battery arrives at the fuse box, travels through the fuse box and arrives at the light switch. I am not sure why you replaced the light switch, but you may want to plug in the old switch and see if the tail lights then illuminate, there are times that a new out of the box compoment is faulty. Check to ensure that both switches are identical. I doubt that you have 6 blown bulbs, (possible, but unlikely) so you need to verify that power is arriving at the switch and leaving the switch.