By the time your unit "shares" power consumption thru that red wire with those other 8 devices ..it is unlikely you will be getting enough clean current to power the unit ...

True you will have 12v ... But the current will be reduced by all those other things also attached to the same 12v feed ...

It's like a garden hose ... It supplies only so much water (current) ... Hooking a 9th spigot to the water hose that already has 8 spigots using water ...is not gonna leave much water for that 9th spigot ...

Rickie