To fix the issue with your 1985 Dodge D100 passenger door, try adjusting the door striker and latch.
Check the door striker: The striker is the part on the door frame where the latch catches. If it’s misaligned, the door may not close properly. Use a wrench to loosen the bolts on the striker and adjust it slightly inward or outward, depending on how the door is misaligning.
Inspect the latch: Make sure the latch on the door is clean and working smoothly. If it's worn or sticking, it may not catch properly. Lubricate the latch with grease or penetrating oil.
Check the door hinges: If the door is sagging, the hinges may need tightening. Tighten the hinge bolts and check if that helps the door close more easily.
After making adjustments, test the door to see if it closes with less force.
Hope this helps! Let me know if you need more guidance.