Where is the relay and fuse for the seat belt located on a 1993 mercury villager?

If you are looking for a broken fuse on this problem, then you are gonna have more than just the belts not operating (dome lights, power Windows and more.) The fuse compartment beside the parking brake release handle contains the fuse for the belts. Something probable is the Inertia switch having high resistance. It will keep both belts on the rear (B)pillar even if you open the doors. To check the inertia switch on the left side behind the cover (you can see a small red button)remove it and use a ohmeter to see if the resistance is close to zero. Try cycling it with a small shock it will open and the just push the red button to close it. Recheck the resistance if it was high.