ok a little history on the issue. Up till about 3 months ago all was working like normal with a aftermarket cd player install a few years before. Then all the sudden the drivers seat vol. up down rocker locked in the center spot and wouldnt move at all. After i removed the headrest contoler and opened it up i found some old soda sticky in side. I cleaned it all up and it returned to a moving rocker switch. But there isnt any sound from the drivers seat nomatter what you do with the rocker switch. So I was thinking it was the headrest controler so I got a good used unit and have the same thing going on. When i hit the main power switch on the headrest contoler i can hear a click... the amp powering up. All the while the pass. seat works like it should. So i said to myself swap the headrest amp... did and no change.... ok so my last idea is that the radio blew a channel and isnt feeding the tunes to the switch and the amp.... changed out the deck... still no tunes. the only thing i havent changed is "Acoustic Equilibration System" from the wiring diagram. I dont know if this is a part of the headrest controler or what or if not where it is at. this is the last thing that hasnt been swaped.
So im wondering anybody know where the A.E.S. is located? and anybody got any ideas on what might be going on?
the A E S is circled in red below
<a href="http://www.flickr.com/photos/badassrx-7/5483857493/" title="vertradiowiring by BadAssRX-7, on Flickr"><img src="http://farm6.static.flickr.com/5212/5483857493_f8107c9291_z.jpg" width="504" height="621" alt="vertradiowiring" /></a>

 

Zombie bump

 

The AES is the vertical unit on the right side of the S4 stock head unit or bottom of the S5 head unit that has the mute button. It is not necessary with an aftermarket head unit since your source the signal for the headrest speakers from the rear output of the aftermarket unit.

Better reference:

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/s5-stereo-install-so-%2Aeverything-works%2A-936255/