My Dad and I do a fair bit of towing, and have to back into some tight spots. That reverse alarm freaks folks out, and is nerve-racking as all get out.
Here's how I fixed it in my Dad's 06; they're kind of out of order, but I'll do my best to describe what I did:
These pictures are taken from the backseat floorboard
Picture 08 shows the seatbelt plug undone, behind it is the one that ties into the truck's harness, it's the splitloom and plug right behind it (it shows you where they're located under the seat)
Picture 03 shows what the inside of the plug looks like, it gave me an idea...
Picture 05 is my low-tech, simple solution, I noticed that the pins in the connector are just about right to fit a common spade terminal. I wrapped the connector with some small stranded copper wire I had leftover from another project to help the connector to fit more snugly over the pins in the connector. I also smooshed the sides down just a little to help snug it up a little more. You want it to make a positive connection.
Picture 07 shows the jumper plugged in. For insurance, I put a piece of 33+ tape over the end, and then a wrap around the plug to make sure that the jumper can't wiggle free and set off that blasted alarm again.
I started up his truck and put it in gear to make sure it works, it did.
Picture 09 is a pic of my Dad's new truck. He's very proud of it, and it looks great.
Thanks for sharing with me how to fix it, and I hope this helps someone else get theirs disabled, that horn honking bit freaks me out.