I have installed a rear headrest monitor system with integrated dvd players and a MOST video/audio interface in the trunk of my car. I originally wired it to the constant hot fuse block in the passenger side trunk as I couldn't find any accessory fuse block in the back. This had the unwanted side effect of draining my battery while the car was off.

So I decided to wire an actual accessory wire to power the aftermarket components. I didn't want to tap any of the existing radio tuner wires in the drivers side of the trunk and so I instead ran my accessory wire to the passenger side front Accessory fuse block by the glove box (see picture). I added my plug and wire into an empty connection and put a 5 amp fuse in.

The accessory power I wired opperates as desired running my MOST interface and headrest monitors and dvd players and turning them off with the ignition (no delay). However I am now experiencing a problem with my MMI 3G unit turning on with the ignition. Previously it would automatically power on with the vehicle. Now it does this only intermittently, and I have to press the power button repeatedly in order for it to turn on. This is a problem as I can't use my backup camera without it coming on right away. It is odd that this problem is intermittent. My next step is to disconnect my aftermarket items from the new accessory wire and see if the problem goes away and also pull codes (see if I have a low battery).

How do I correctly wire the accessory power in this vehicle?

Should I use the new wire to just power a relay in the trunk and isolate my components from accessory power? Could the MMI shut down be due to my added aftermarket components possibly draining the power from the MMI through the accessory wire during delayed power off? Could the battery management system be kicking in to shut down the MMI to save battery power?

Thanks for your help!