conFUSEd about Trailer Lights

I have a 2008 Tacoma Double Cab with the TRD Off Road package.
I noticed last fall that my tail lights on my trailer weren't working.
The turn signals and brake lights work fine.
I checked the bulbs and made sure that they were good.
The led lights on the 7-pin to 4-pin adapter plug will light up for the brake and turn signal lights, but not the tail lights.
I then took a multimeter and tested the power coming through the adapter to confirm that -- still no tail light power.
Then I tested the pins in the 7-pin plug.
It showed the same thing -- no power from the tail lights.
The tail lights on the truck work fine, though.

I've been unable to find a fuse for this, if there is one.
From what I can see from the electrical spaghetti leading up to the trailer light receptacle, the lights are spliced directly into the tail lights on the truck.
Am I missing a fuse somewhere?
I can't seem to find anything under the hood or under the instrument panel for the trailer tail lights.
I've looked under the back seat in the jack compartment (someone posted that they found theirs in that area) and came up empty.

Before I take it into the shop, I need to make sure that I'm not missing something.
A bad fuse would not be covered under warranty and I don't want to pay the bill for someone changing a fuse.
But if it's a problem with the wiring, I should be covered under the warranty.

Does anyone have any thoughts or ideas for me to try?
I'm going to double-check all of my fuses and make sure I'm not missing something.
On that subject, is there any place I can go to find a more detailed description of the fuse layouts?
The abbreviations on the panels are of little help to me.
Thanks!

 

I can't confirm it right now, but I am about 90% sure there is a fuse labeled Trailer Tail Lights (abbreviated). It is under the hood in the fuse box behind the battery.

 

underhood fuse box,check all fuses with test light esp #9 #18

 

Yep, there it was....right there in the fuse box behind the battery.
I should have opened my eyes the first time.
Replaced it and now it works!
Thanks for the responses.

 

+1 for creative thread title. conFUSEd