Dim Panel Monitor

should i ground my car monitors to bare metal, or to the black wire the head unit is hooked up to?

i have four monitors, two in the headrest, and two in the visors. i have all four of them grounded to the black ground wire that the radio is hooked up to in the dash. should i ground them to bare metal instead? they have been dimming lately the more i turn up the volume in my head unit. also, ive heard that a good power source could be found in the fuse panel. how would i find and hook up a power source there? thanks yall for any input.

I wouldn't use the ground from the head-unit. Just run your own ground wire from either the chassis or battery.

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