I connect the parking brake cable to a ground , the video is working fine but , when i turn my head light on the screen change to rear camera n i can do nothing whit until I turn the light off . What can I do ?

https://www.carcareninja.com/tail-lights-not-working-but-brake-lights-are/#:~:text=The%20common%20causes%20the%20tail%20lights%20do%20not,it%20does%20not%20allow%20the%20circuit%20to%20complete.
This post has a few suggestions that may help you find your problem.

Did you check the common return? Most of the time it is connected to the chassis of the car. See if anything is lose or corroded.

Change the bulbs.

Looks like a bad connection to the ground frame or to the Batt cable ,mainly the Neg cable inside the Batt box,. a common issue for the sporster!

The front park lights work correct? If the front park lights work than there is not a problem with the light switch since the brown wire from the switch supplies power to the front park lights, front side markers, and the rear taillights. There should be twelve volts on the brown wire from the headlight switch with the connector plugged in and the park lights turned on. If this is true that there is a problem with the wiring to the back of the vehicle. A thorough inspection of the harness should reveal the problem. The dim break and blinkers support the above. High resistance also know as corrosion, in the wires or connections would cause this problem.

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I ran across of alot of lcd head units that requiers the parking brake wire connected so it will show the video, (usually just audio if parking brake not on). But if you connect that wire to a proper ground (screen always on) or a grounded switch so you can control it maually (turn it on or off when you choose)

no disrespect but....
Check the book and make sure you are using the proper bulbs on all sides. (3957 looks just like 3956 but wont work right)

check power on rear light positive terminal.rear light fuses,or ground,..lee

Connect the light blue parking brake wire coming out of the back of the radio to the black ground wire also out of the radio to the black ground wire on the wiring harness.... Basically just ground the parking brake wire.. Itll work, I promise. I have the 7001u.

You have to bypass the Parking Safety feature. Here is the info I have found. I have not verified it myself for accuracy, so use at your own risk. AVIC-N2 lockout bypass: Underneath the MAIN unit (not the hideaway) is a small silver sticker, peel this back. There are two contacts with the label "R197". Drop a bit of solder between these to connect them. Also, you must ground the Parking Brake wire.