Mercury premium headache

I am in the process of dropping a new Pioneer head unit into my 1990 Mercury Grand Marquis Colony Park wagon. The thing has the premium JBL system installed, but not the one shown in any chart I can find.

The old head unit is a basic Ford tape player with the corresponding flat black and grey eight-pin plugs on the back instead of the normal premium setup with the one square black plug with the flat grey one.

I dug the pos stock amp out from behind the spare tire in the wagon's cargo section looking to use a bypass jumper from Metra. No love there. The amp is about the size of the palm of my hand and, instead of the two flat plugs the bypass cable uses it has two of the older square style plugs.

but wait, it gets more fun.

The radio has eight speaker wires going out, but somehow, there are only five input wires going into the old amp — so it is using a common ground. I have no idea how the wiring harness drops from eight to five speaker wires between the head unit and the amp. The amp has all eight speaker wires going out of it, and I have poped and tagged them.

I hooked up the Pioneer to the stock harness using Metra adapters and it powers up fine. I need to create a manual bypass at the amp, since running new wires in the wagon is not feasable because Ford, may they rot, has made it almost impossible to get around the mechanical components where the back seat folds down. A mechanic buddy says Ford intentionally started making cars dys unfriendly so everyone would have to use their shops. Having worked on this thing for a number of years, I believe it. You have to pull the steering column to get to the dash components.

Any ideas what the pin output is on the head unit side of the wiring for the amp?
It is an eight-pin square plug, and it appears three of those wires are for power and grounding, at a guess. The other five are speaker, but I'm getting some weirdness doing a trial and error patch. The wire colors in no way correspond to the wiring harness at the front of the car. According to the crummy schematic provided in the Haynes manual — which does not tell you what any of the wires actually do — the wires to the back are actually several different wiring harnesses spliced together.

Any suggestions?

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There is nothing so stupid that someone, somewhere, won't do it

Alright this is what I came up with.

the black connector should lead to the stock amp and the gray connector has the wires power wires

the black connector:

Right Rear Spkr (-) Blue Purple w/ Black Stripe
Right Rear Spkr (+) White w/ Blue Stripe Purple
Right Front Spkr (-) White Gray w/ Black Stripe
Right Front Spkr (+) Blue w/ White Stripe Gray
Left Rear Spkr (-) Red w/ Blue Stripe
Left Rear Spkr (+) White w/ Blue Stripe Green
Left Front Spkr (-) Blue w/ Orange Stripe
Left Front Spkr (+) Purple White

Gray Connector:

Amplifier Can't remember the color but it is the wire opposite of the +12V wire
Ground Wire Black
Dash Light Dimmer Wire Orange (if available)
+12 Volt Ignition Wire Blue w/ Black Stripe
+12 Volt Battery Wire Blue w/ Red Stripe

Hope this helps

most fords have a bypass harness near the radio cavity. after the radio is pulled, check to the right and left of the cavity.  if you have it, it will be for the gray and black plug. both the male and female sides accordingly.  use the "L" side for your power and speaker outputs.

example, '90-95 escorts have the bypass harness in the back of the radio cavity under a metal housing.

example, '90-'93 mustangs have the bypass harness above the radio cavity and behind the heater controls.

example, '87-'90 thunderbirds have the bypass to the right of radio cavity.

  the t-bird and mustang factory amps resemble the shape of a "football". if your amp also resembles that "football" shape, then the bypass will only do 4 out of the 6 speakers you have. the doors and the dash are wired in series and the rears are out of phase according to aftermarket color code. i'm pretty sure you will have to run speaker wire to the back speakers. sorry, but it's been awhile since i've been in an older ford/merc. hope this helps, good luck with the install!

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do it right the first time....less warranty work=more money!:)

oh yeah, you're right, that is a common ground amplified system. also, you can use a converter to intergrate your pioneer deck without backfeeding the amps. the last one i used i got at best buy. it cost about $40.  it was called "the install edge". iecps2.

  good luck!!!!!!!!

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do it right the first time....less warranty work=more money!:)

go to an electrical supply store, buy a spool of wire, like 500ft. for 12 bucks, and take an afternoon and hardwire it. the stock wiring blows anyway, especially since its a ford.

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Pete - SPL Enterprise Inc.

Must agree with pete. it's not worth the headache to figure out the wiring.

OR you can replace the factory amp and speakers with aftermarket stuff and put an LOC on the output from the speaker wires coming from the pioneer head-units speaker output to the factory amp's input. You might run into noise problems with this idea though so I just reccomend getting some good speaker wire from some one like Stinger and re-run everything. Factory wiring sux and its no bigger then 18 gauge.

Thanks for the help.
I may just bite the bullet and run new wires, though it will not be a beautiful install job. Getting to the spaces in this antiquated luxury Merc station wagon is all but impossible.
Of course, since I use it for work, instead of as a Griswald family roadster it was designed to be, I will probably opt for running wires in some sort of coping along the side of the tunnel.
It does not have to be pretty, just sound good. After all, what is a car but a fancy transportation system for a really good stereo.
It's especially important in Talladega, AL, given some of the music tastes around here. I feel the need to re-educate the public.
Besides, given the stress of working as a journalist, if I don't have sound in my ride soon, it will be clock tower climbing time.

Thanks again.

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There is nothing so stupid that someone, somewhere, won't do it

griswold family wagon lol!!!!!!

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Pete - SPL Enterprise Inc.

just a thought............if you find it difficult running wires at the bottom of the vehicle and under the carpeting, maybe it might be easier running them up the "A" pillar and along the roof (between the headliner and roof) and back down the "C" pillar.  JUST A THOUGHT...........just a thought.............JUST A THOUGHT...............just a thought..........JUST A THOUGHT................. use at least 16 guage wire for your run.

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do it right the first time....less warranty work=more money!:)