Adding a backup camera to a 2017 Journey. Sounded pretty simple. Got everything hooked up but not working properly. Tapped into backup light wiring to power camera when shifted to reverse. Image on screen blinks but does not work. I put a volt meter on the + & - wires going to the bulb & getting fluctuating readings between 11 & 12 volts. If I hook the camera wires to a 12v battery everything works. Seems like I am not getting a strong 12v from the bulb wiring. Any ideas?