Fox Mustang Radio Wiring

Grabbin' Asphalt

5 Year Member
Jun 10, 2013
Atlanta, Ga
So I have a 1990 mustang that had the football shaped amp from the factory. It was removed when I added an aftermarket radio. I've had 2 aftermarket radios installed by 2 different audio places over the course of 20 years. The 2nd one has been in for 12 years along with amp and sub wired to the hatch cargo area. I'm about to install a flip out radio with gps so I went in to see what wiring was done back in the day.

1. There are 2 rectangled plugs and 2 grey square type plugs. The rectangled ones are black and grey. From what I've read black is supposed to the speakers and the grey is constant power, ignition, antenna etc...

The 2 square grey plugs I believe are the amp wiring, amp power and the other plug is more speaker wiring from the amp.

So I went ahead and bought the radio harness plugs that are the 2 rectangled plugs cause i was at best buy and thought since i was there I'd go ahead and pick it up to do it right.


The wire chart here shows the speaker wire on bottom-the black connector and the upper part is the grey wire chart. These connect "TO YOUR HARNESS" from the headunit plug wired in.


Then when i got inside the dash i found the black one not being used and the grey one tapped into-2 wires only and the speaker wire hooked up to one of the square amp plugs. So now I have a new wire harness I cannot use cause they are not being used now, unless I want to go deep into this project. I will probably just take the harness back.



This is the already installed headunit wire information that is the very small plug in the upper pic, lower right.


Hard to see in the pic cause I cut it off but the lower square plug is NOT being used, wires are cut and capped, the end plug one on top is the one BEING used, it connects to the connector where my blue screwdriver is pointing. Then the speaker wire runs to the very small head unit plug.


So as I'm seeing this I'm really thinking i will leave it how its wired because the sub and speaker wires are working fine and I've had no issues with that plug in 12 years. So looks like i will will tap into those from the wire harness of the headunit already installed when the new radio arrives. So as it sits, i will just tap into the constant power, ignition etc cause its really easy to decode with the one already installed. I will never sell the car so i'm cool with it. But maybe this can help someone else if they go in and find jacked up wires, so it can be wired in this way and mine has been this way for 12 years, hope this helps some one else.
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I went through the same thing recently when installing a new sound system. My LX had all stock sound system with head unit and power unit as separate pieces.

I thought I could just buy plug and play harness and make it all work. I was wrong. After lots of study including trial and error, I wound up having to hack into the factory harness anyway.

I remember it being somewhat confusing since wires would change colors from one harness connector to the next.

If your system was working and you are just upgrading, I concur with your decision to follow the lead of the last installer. Just make good connections and everything will be fine.
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And if anyone cannot see the wire colors that are tapped into on the grey connector, they are (1.) green w/ yellow strip (2.) Yellow/ black stripe. Using the already installed headunit wiring chart on the radio, as in the pic above. Those two wires are connected to chart #1-red wire is the ignition switch= Yellow w/ black stripe(on grey connector) and the chart #16-yellow wire is the battery lead constant=Green w/ yellow stripe(on grey connector).
If anyone is wondering, the remote on amp wire leading to the sub amp was tapped into the #1 red ignition switch wire. A separate amp direct power supply still runs directly to the battery from the amp with fuse.
ya ...just leave the old harness on and cut after it and connect everything to the same colors and your good,if all works why change it...
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I actually ran my own wire and saved myself the confusion. The only things I have hooked up to my head unit is the necessities such as power and signal on. I have all my new wires running back to my amp. My harness was hacked up to begin with and I didn't feel like rooting through the garbled mess.
Maybe this will help...
or confuse you more...


I found this too, but just looking at the grey plug and black plug wires the colors are different. It does appear the location is the same but the colors are off. "P" and "N" are the ones being used and tapped into and they do show the same information as the already installed headunit. So I believe plug orientation is the best way to decode the plug when using a probe tester, but i just recounted the physical pkug wires and slots and they are sill diffrent, my "I" slot is different too.
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Black plug looks different too, I have got a white w/red stripe on my black one and the other colors seem different too :rlaugh:

I am certainly not gonna' open a can of worms here, when the new unit comes in I'm tapping into the chart #1-red ignition and #16-yellow battery lead, #8-ground and the speaker wires from the Front-#4 thru #7 and Rear #12 thru #15 on the already installed unit and leave it be :rolleyes:
BTW, when I said I hacked into my harness, dont get me wrong. I meant spliced and I did a neat job of it. But I'm sure you all understood that. :D
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