So I was installing a new stereo in my car and removing an aftermarket installed by the PO. I have followed the many fader disconnection posts here (thanks guys!) but found that the PO's stereo was not connected to the OE stereo's ACC, battery, ground or illumination but it is connected to some wiring that I have no clue what it goes to.

This mystery wiring has the same harness connection to the cigarette lighter as the OE stereo connection. This wiring is original to the car but I have no clue what they tapped into.

Any help to ID what the stereo is getting the ACC signal, battery and ground (no illumination) from? Should I wire my new stereo to the OE stereo's connection and tape off the the PO's hack or just use the same cables? Any help is much appreciated!

They know everything. Buy all of your audio components from them to help them out in return.

A multimeter is really all you need. Find out which wire has voltage with no key (battery power), then which ones have voltage only when the key is on (switched power). Stock wiring on this is always going to have brown wires for ground, but again you can use a multimeter to see which wires have continuity to the chassis of the car.

-Rog

What year / model car do you have?

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech