(NOTE: I thought I had managed to save this response to a previous thread on backup lights but it seems to have vanished so I will try starting a new thread)
GOAL: I wanted to add backup lights to our 2004 International
PROBLEM: The wiring diagram in the manual shows that a yellow wire goes from the TV connection pigtail to a black wire (no indication of where the color change occurs) which goes back to the tail lights. After much looking I was able to locate the box where the running/tail lights connect inside of the bow (we live on a boat - sorry but I find nautical terms helpful for descriptions like this) - the initial pigtail terminates inside of a box under the port (left) side of the frame and then similar colored wires continue up into the trailer. Inside of the port bow wall there is a black box accessed (in our trailer) through a hole under the couch/bed (where I can't fit, so I added a new access hole under the port side seat bow end). Inside of the black box all of the wires connect to wires that go here and there to the trailer lights EXCEPT for the yellow wire which ends on a stud and goes no further. In the back of the trailer I found a black plastic box behind the tail lights. I had to literally tear into the plastic to get enough access to pull the wires up and I eventually found a black wire which was dead headed. I later found that the black wire did go between the two sides but only went about 2 ft forward and then ended. SUMMARY: there was no wire running from the connection box at the front of the trailer to the black wire at the back of the trailer.
RUNNING THE WIRE: Thanks to a previous post by Boxite I learned that the key to accessing the harness in the back of the trailer (rear toilet model) was to remove the shower panel to the left of the toilet. The harness runs between the visible grey water tank and the wall and can be reached with a hook to pull it up into reach). I cut the entire harness at the left tail light and used it to pull a string back into the toilet area then I used the string to pull the new backup light wire and the rest of the harness back to the light (yes it required a lot of wire connector to redo the wiring (which curiously uses soldered connections)). Then a wire snake was run forward to the access panel under the vanity > on to where I could access the wires under the wheel well cover box > under the wire channel that runs along the base of the wall under the dinette and eventually into the connector box to join the yellow wire.
NEW TAIL LIGHT: Rather than cut a new hole for the backup lights I switched out the original lower LED tail/stop light for this setup from Amazon. I had to use the original rubber gasket, DW40, and a rubber mallet as the lights are a slightly different shape but they did eventually fit the holes.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 (BEWARE: the new light uses a different color code than the original (original used white as ground the new ones uses black as ground.)
After all of that the lights were connected and tested - now if my welcome to Canada quarantine will end we will test them at a campsite.
Norman