my sony hu has 3 blue wires, why?

my current hu is crapping out so I plan to swap in my old Sony XRC7200 problem is I don't have the install manual anymore all the speaker wires are labled, so thats good But oddly there are 3 blue wires one is marked "ANT REM MAX 0.1A" (I know this for activating the antenna) and one is marked "AMP REM MAX 0.3A" ( I know this is to run on the amp) but there is also a light blue wire that is unmarked, which is puzzling me, any ideas what it might be? (I also have a orange white wire for illumination) could this possibly be a dimmer wire? thanks

I seem to remember that they were a loop to control a separate signal source.  A stand alone CD player maybe.  Or a stand alone cassette player.  You do not need to use either of the ones to the left of your picture.  Just plug them to each other or insulate them so they do not touch ground.

thanks

I think that is Attenuate...At least on some of the Sony's light blue was ATT.M.E.C.P & First-Class

Go slow and drink lots of water...Procrastinators' Unite...Tomorrow!

tommy... wrote: I think that is Attenuate...At least on some of the Sony's light blue was ATT.

what does ATT do?

Attenuate = Reduces the sound a bit.

i am an idiot wrote: Attenuate = Reduces the sound a bit.

A longtime lurker, this is something I actually know about. :D You use this wire to patch into a vehicle harness that supports OnStar and various other built in cellphone systems. It signals the Sony HU to momentarily stop sound output to allow you to hear the phone/OnStar audio, etc.Life is too short to build slow computers or weak audio!