How do you replace the rear turn signal bulb located on a 1993 Nissan truck?
If it is like my 94, simply lower the tailgate and look to the right and/or left and you should 2 bolts in the corner of the bed on either side of the tailgate. Loosen these bolts and the light assembly should pull free from the body. On the back of the light assembly there should 3 connectors, just twist and pull which ever light you need out of the assembly. To re-install, reverse the process.
You may have to get under the bed liner if you have one to access the bolts.