How to access dimmer wire
 

I can't find information on accessing dimmer wire for my aftermarket head unit and AEM gauge dimming.
I've read you use the middle wire on the dash dimmer but I don't know how to gain access.
I've also read the orange wire on the OEM head unit harness is for dimming???

Any helpful hints??

Thanks.

This is for a 2009, all I could find.

https://i.imgur.com/giGD8Og.png

dimmer
 

I'm just going to just use the dimmer wire going into the head unit.