Regarding trailer harness wiring...
(I will try to update this post with more pictures)
I decided that I wanted a 7-wire isolated trailer wiring module to protect the truck circuits from any issues that might occur in trailer wiring. These modules source power directly from the battery and don't draw any real power from the lighting circuits so they won't impact them. I found one mine on etrailer.com. There are several, but I went with P/N 22551. This one has a pretty high current capacity to drive trailer lights including backup lights (not all modules have separate current ratings for backup lights). This module also has the wiring for integration of an electronic brake module should I want/need to add one in the future. Price seems to fluctuate, it was $65-70 when I bought it a month ago, looks to be about $115 today.
Install...
As I tore into my 2000 TLC which already had a 4-position harness installed (I believe it was factory or port installed), I found that it already has a module that I presume does the isolation I described above. This module is installed inside the body, above the left rear brake light assembly. I decided I would leave this module installed since it was already tied into the needed circuits (left/right turn & brake, running lights) and has the outputs I needed to feed my new module. Even though the brake module is sealed for weather, I installed inside the cabin anyway, plus the circuits are already there. I mounted the new brake module in about the same area, there is easy access from inside the truck, behind the jack location. I mounted with 3M VHB tape to the outside wall. I'll try to grab a photo.
For the backup light signal, I used a T-Tap / splice to tie into the backup light signal going to the left rear light assembly. I believe it was a red/blue wire. I tapped into the harness on the truck side of the connector so that I could still unplug the light assembly and remove when needed. This is easily accessed from that same location behind the jack.
For the Left/Stop, Right/Stop, and Running Lights, I used the outputs of the factory module that went to the 4-pin trailer connector. I removed the existing harness, it has a Deutsch connector in behind the light assembly. I pulled the harness off the truck completely and cut the connector off to reuse for the new trailer module. To pull that harness out of the truck body grommet, I needed to remove the connector. To remove Deutsch connectors, just pull the orange or green plastic part out of the front of the connector (might need to have a little hook to pull it out) and then you can access the retaining tabs to release the pins.
NOTE: In order for the factory module to function, Pin 4 of the output needs to be grounded. I put a ring terminal on that white wire and used a bolt in that back area to ground it.
For cable routing, I followed the same path as the original harness, which exits the truck towards the bottom, behind the left wing of the bumper. See photo. I punched a new hole in the grommet for the power and ran the power all the way under the truck along the frame to the engine bay and connected directly to battery with the fuse holder included in the trailer module kit. I used some butyl rope to seal around the cables at the grommet. I ran the 7-wire output from the new trailer module out the same grommet and spliced those outputs to the harness that came with the bumper. I connected same colors of wire together.
NOTE: I learned that not all harnesses use the same colors for the same functions. These colors are not standardized. There seems to be 2 different conventions (RV and Traditional). What
is standard however, is the function-to-position relationship in the connector. All connectors have the circuit functions in the same position, and they are also marked on the trailer connector cover that comes with the bumper. In my case, (same as
@suprarx7nut ) green and brown were backwards. I ended up just pulling those 2 out of the connector and swapping them. Pull the blue part out of the connector and you can then access the tabs to release the pins from the connector.
I also decided that I would drive the bumper's backup lights off the trailer module, so when I spliced the trailer harness to the module, I tied in to the backup light circuit (yellow for me) for the bumper lights. I did this so that they wouldn't put any additional load on the existing truck wiring, although I'm sure it wouldn't be an issue. Just an extra measure of isolation. I put connectors on the bumper's backup lights. Certainly useful if you ever need to remove the bumper. Lots of choices out there for connectors. Toyota uses Deutsch connectors if you want things to look factory.
Additionally, I picked up a 7-pole to 5-pole adapter from etrailer.com for $14. P/N A75TB. The 5-pole connector will also accept 4-pole trailer plugs. There are lots of adapters, this is just the one I went with. There are also adapters that have both 5- and 4-pole plugs. If I towed with a 4-pin trailer a lot, I would get one with only 4 pins so that there isn't an extra pin exposed to the elements.
Hope this write-up is useful to someone, I can answer questions or get additional pics if people need.