2015 Toyota Tacoma Taillights

Okay so before I get blasted for not searching I searched I've read I've checked. Here's where I'm at:

PROBLEMS:
#1: Tail lights aren't getting voltage. Checked at the plug with a meter.
#2: Tag lights are dead too
#3: CEL For low voltage to Heater Control Circut, P0037***

More Info:
Parking, brakes, backup, and hazards work. Checked factory OR Tow plug getting correct power.


Steps to Correct:
#1-3: Checked and replaced fuses, checked bulbs, checked housings with direct fed 12V, they lit up.
#4: Cleaned up Tow Plug of any mud.
#5: ***Bought brand new Optima Yellow Top D27F, CEL got cleared waiting to see if it comes back.


Still Investigating:
So its been narrowed down to wiring issue YAY if I wanted wiring issues I would have bought a chevy... So where I need your help. Where are the common places to check for wiring issues to the rear? Anyone know where the splitter is for the tow package (is it even a splitter or does it have its own wiring?) The threads I've found don't seem to follow up with their solutions. I have a little under 78k on it with the extended warranty but I don't suspect it will cover wiring I got the platinum warranty until 125k I'm trying to avoid the dealership route if its a quick and easy fix with your help. But work over night so most of my driving is night time not good when you can't get your back to light up lol. Thanks for the help in advance.

 

Updated, took it to the dealership, they determined there was a break in the wire harness that runs along the frame SOMEWHERE so they Replaced the whole harness since they couldn't find any damage. It's fixed now and the extended warranty took care of most of it for me. I had to pay them to take off the sliders and skids and put them back on (warranty wouldn't pay for labor for aftermarket parts I will gladly accept that.)