There are two ways to deal with this. Do it on the cheap or do it right. Both work fine. You are probably reading this because you have that annoying "tail" indicator on your dash. Most likely one or more sockets are corroded. The first thing to do is fix the leak in the tail light lens that caused the corrosion in the first place. Once you are certain that this has been done satisfactorily you need to determine if the offending socket is salvageable or too far gone and needs to be replaced.
The right way to fix it is to purchase a replacement socket from Nissan or the autoparts store. They come with "Pig tail" wires to splice into the existing harness. Cut the harness wires close to the old socket and splice to the appropriate wire on the new socket one at a time so you don't mix them up. Use a "butt" or "blind" crimp connector (Click Image at Left), wire nuts or even twist them together and solder. DON'T just twist the wires together and leave them. You'll be asking for trouble.
The cheap way. If the socket isn't too badly corroded you might be able to reuse the same socket. This is what I did. I cut the wires to the socket and removed it so I could work on it easier. I took a dull X-acto knife and scraped the inside of the socket until I had clean shiny metal all around. I also restored the two tin contacts at the bottom of the socket by resoldering them. This is a little tricky because there is a spring in there. Push down on the disk and support the wire from the back while you solder. Otherwise the disk and spring will go flying one way and the wire will fall out the other way. That's all they are anyway in the first place is solder beads so soldering works great. Splice the socket back in to the right wires. Before inserting the bulb into the socket, coat the bare metal on the inside of the socket with axle grease or silicone grease to prevent further corrosion. This should then work just as well as a new socket.
Dead Tail Lights. Here's a hot tip from Seth Herstad. According to Seth, his tail lights had gone dead and couldn't find the problem until he looked at the tail light sensor, the 1x3 inch white plastic box on the right side tail light assembly. The tail light sensor gives you a warning light on the dash when one or more tail light bulbs have burned out. It had detached from the tail light assembly and was hanging up-side-down. Water from the leak at the top of his tail light ran down the wires and into the sensor. His sensor was corroded and knocked out his tail lights. Once he replaced the sensor the tail lights worked again. Thanks Seth!