Right Taillight Not Functioning...

Not knowing the year of your ride, it's hard to tell, but I'd research by year and model to see if there's a common ground for all of those bulbs.

Nathan

+1 on above. Check the ground (but not in the way that you think). However I happen to know that both sides are grounded at the same point in the trunk. So for the ground to be good for one side and bad for the other would have to mean a break in the wiring harness.

I believe the actually green grounding bolt is on the left side of the trunk. It will be necessary to remove the trunk liner.

The wiring harness passes from right to left near the license plate from inside the trunk. If this were my car, that's the first place to look for wiring harness damage.

If unable to find obvious wiring harness damage it time to get out the Volt-Ohm Meter (VOM). Use the VOM to test for +12 volts on the left side using a known good ground (the green terminal in the trunk for example). Once voltage on the left side has been confirmed, test for +12 volts on the right side.

Once +12 volts has been confirmed on the left side using the known good ground, re-test using the ground inside the socket. Should this test fail then the diagnosis is confirmed. It now becomes a matter of finding where the actual break is.

Ok. Now things get "real".

If this were my car the next test is to verify there's power coming out of the multi-function switch OG/LB wire.

If there is power, then there's a wiring break in the harness. The wire path passes through several connectors (C202b,C265, C314, C408, C4114). Test the OG/LB wire at each connector to find out where the power stop. While there inspect each connector for evidence of water, rodent, mechanical damage.

This is where having a full set of Ford wiring diagrams are almost a must. Just too much information to post. If interested in getting a set for yourself I maybe able to help. PM if interested.

See what I mean about "getting real?".

If there's no power out of the multi-function switch OB/LB wire with the right turn signal activated then the problem HAS to be in the multi-function switch. Note, this seems unlikely to me because the dash turn signal indicator works.