hi i have a 2012 f150 harley davidson addition and i want to tap into factory harness behind radio for rear cam screen to add a camera for my trailer when backing up my trailer anyone with any input

 

I added a whole system with a screen in the rear view mirror. Camera in the tailgate handle

 

Are you trying to reused the factory camera feed ?
- Is there one already installed ?

Just want to clarify what you are trying to do here.

 

If you are trying to do 2 feeds from 1 wire -- this is impossible.

You will need to run another cable to the rear.

 

yes im trying to have 2 feeds one from stock tailgate then another one when my trailer is hooked up i can have one mounted to trailer i under stand cant have 2 signals coming in so i was going add a switch for when i want to use trailer

 

My question was a bit vague.
I was talking about the the factory camera wiring, but I think I am clear now that you are trying to reuse the camera display in the factory head unit, and rerun a new wire for the trailer camera.

The Color codes at the Front Display Interface module ( FDIM ) are :

REar Camera video + = White w/ Green Stripe wire.
REar Camera video - = Brown w/ violet stripe wire.
Shield wire is Black It should be right at the back of the FDIM

I do not know what the video levels are on the + & - rear camera video feed, so you will need to test this with an external display to make sure it is not too "hot" a video feed for the FDIM.
- I think it is pretty much standard, but this is jsut a SWAG, I cannot say one way or the other 100% certain.