Left rear tailight/brake light not working.tried 4 different new bulbs,checked fuse block under hood and under rear seat>All other lights functioning.Replaced bulbs on right rear side 6 mos ago.Any suggestions on where to look next.

Tony, our TB's only have 3 bulbs, 1 brake, 1 running, 1 backup.
If you happened to be playing with NEW LED bulbs (from local retail location) for the brakes, guaranteed you blew the fuse under the rear seat. It takes a special CK socket for the brakes that no one carry's. If you're only dealing with normal incondecent bulbs, I'd still check the fuse under the rear passenger seat.

Did you check STOP LP fuse 15amp. in the rear fuse block ? Do you know where this is. Fuse Block - Rear Under the rear seat, on the left side of the floor pan.
The STOP LP fuse in the fuse block - rear supplies battery positive voltage to the normally open stop lamp switch. When the driver presses the brake pedal, the switch contacts close. The battery positive voltage flows to the left stop lamp assemblies, to the right stop lamp assemblies and to the center high mounted stop lamp (CHMSL). The left stop lamp and the CHMSL have ground at G402. The right stop lamp has ground at G401.
Did you check for power at the stop lamp switch ? both in an out of the switch with brake pedal pressed ?
Did

put a prybar between seat and brake pedal and use a test light on the wire in trunk where bulbs are sometimes bulbs look good but aren't or you got wrong bulb. a test light will verify that and make sure test light lights

Check your Tailight fuse to see if it's blown, if so then start checking for a bad bulb(shorted element) in tailight circuit boards . and also don't forget to check grounds as well, there should be one at rear frame by left (drivers Side) tailight connection/trailer harness connection. hope this helps. do your Brake lights Work ?

did you check the VEH STOP fuse? #34, 15 amps, in the rear fuse block, under the left rear seat.

The fuse block that contains the brake light relay is under the left side of the rear seat.There is also
a fuse block under the right side of the rear seat. Another behind the dash under the steering column. And one more under the hood right front corner of the engine compartment. If the relay is
good, check the brake light switch for constant 12v in and 12v out when peddle is pushed.
The brake light switch is under the dash at the top of the brake peddle. Hope this helps.

Make sure the fuses are good.There is a fuse for left and right brake lights.The fuse blocks are under the hood and there`s also one under the drivers side rear seat.If the fuses are good then remove the rear lamp assembly and check the bulb.I believe there are 2 screws and then just pull lamp assembly out.Hope this helps.Good luck.

The body mounted brake lights, are on a different fuse than the upper light. Check fuse #12 a 25amp fuse in the fuse block under the hood on
the left fender. The upper light fuse #16 a 10amp fuse in the rear fuse
block, under the left side of the back seat. Hope this helps.

You will need to check the contacts where the bulb inserts for arcing, causing a short. Test for power and ground at the conn. 2 b sure you have power there. If this is the case you will need to replace the light assembly.

check the wiring from the tailights back to the fuse panel, it sounds like an open connection. if i recall correctly check under the dash on the drivers side near the fuse panel for a bunch of wires in a bundle and look carefully for a wire or two that are cut/shorted/or seperated, you can also check under the drivers side kick panel by the hood release.