Backup camera head unit connection headache

So I got a 2011 that I put a Bluetooth touchscreen head unit out of a 2013 in. Swapped over everything no problems a while back. Now the rear view camera install is gicing me grief. I bought the 24 pin connector for the rear of the HU. Split the signal going to the rear view mirror down behind the ebrake kick panel. Patched in some shielded cable to the deck. But I can't figure out the pin out formation on the back of the HU. Can someone help me out pls. Im getting frustrated.

 

Anyone else install a oem touch screen into their 2011 or earlier Taco? How'd you do the back of head unit connection from the rear view mirror feed?

 

Copied for InTheRough's post

 

Camera Source makes a plug and play harness that will do this. You need to read my post.

https://www.tacomaworld.com/threads/how-to-find-your-reverse-trigger-wire.416056/

 

I was in the understanding that the connection was made in the r15 24 pin connector though

 

R15 pin 2 would be the reverse signal. top row pin second from right

 

OK got it. So what is pin 15?