On BlackVue's Dashcameras with rear window camera (2 ch.), This is the cable between the windshield camera and the rear window camera.
The cable can be stored in the cover of the car and pulled between the two cameras.
Coaxial video cables for two-channel BlackVue dashcams, compatible DR750-2CH LTE, DR900X series, DR750X series, DR900S series, DR750S series, DR650S series, DR430-2CH, DR470-2CH.