1985 928S Stereo wiring

[PC-85-928S]

My 1985 928S came with an aftermarket Pioneer DEH-720 stereo.
It was fine for me.
I am not interested in loud crazy stereos, and have no desire to further complicate the Porsche wiring.
However the unit did not light up any more.
I bought a Blaupunkt Madison CD127 on ebay, and had my mechanic wire it in.
Something was not right, very poppy, and speakers were cutting in and out.
My original amp is still in place next to the passenger seat.

So I pulled the Blaupunkt out this morning and I am starting over.
I do have the factory wiring diagram, but it is a bit confusing.
Can anyone help me identify these wires



I see a small wiring harness with a small red and brown
then a larger harness with
thin red
brown & white
thin brown
thin white
2 more thin reds
red white
thick brown

plus the antenna wire with a thin black attached which i think is the antenna booster

any help appreciated

[PC-85-928S]

CORRECTION:
Big Harness:
thick brown
thin brown
thin brown/white
thin wht
2 thin reds
thin red white stripe

[PC-85-928S]

after studing the wire diagram 1000 times, and looking behind the amp
for the wiring colors
I realize everything leaves the stereo in only 2 sets of wires and goes to the fader
in RED/BROWN &
RED WHITE/BROWN WHITE

have to find out which red is speaker

[PC-85-928S]

[Pete R]

The wire running with the antenna wire should be the trigger to raise and lower the power antenna.
If no one can identify the rest I will check my manual when the kiddo is asleep. I'm pretty sure the thinner wires will be for the amp. btw.. the brown and white in the lower part of the pic looks like the casing is gouged off, mighnt need to get some electrical tape on it

[MPDano]

Are you sure those a re stock speakers? I thought they all came with Blaupunkt Speakers (I stand corrected. I see a 928 part number on them. ITT?).

Anyways, you should be able to just follow the wire colors and what they go to. I ditched any stock fader control and wired it up so the stereo can handle this function.

[PC-85-928S]

hooking up an external stereo I can get audio if I go directly to the speaker connections AFTER the amp, but not through the RED/BROWN & RED/WHT STRIPE. BROWN WHT STRIPE at the dash.

I am considering by-passing the amp and running 4 sets of speaker wires from dash to connections after amp.

One speaker not working on passenger door.
I may have to take off door panels.

I have been trying to avoid that.

[Pete R]

I am not 100% familar with the stock head/amp system...but. normally you can't bypass the amp. The head unit is sending out a low voltage "pre amp" signal not one powerful enough to drive a speaker. You need the amp to power the speakers, the head unit won't do it. Which makes sence from what you descibed.

[MPDano]

Originally Posted by PC-85-928S

hooking up an external stereo I can get audio if I go directly to the speaker connections AFTER the amp, but not through the RED/BROWN & RED/WHT STRIPE. BROWN WHT STRIPE at the dash.

I am considering by-passing the amp and running 4 sets of speaker wires from dash to connections after amp.

One speaker not working on passenger door.
I may have to take off door panels.

I have been trying to avoid that.

Door Panels are some of the easiest things to pull on a 928. Your in for a treat if you think this is difficult

[riber.bentsen]

You don't have to pull the door cards to check the speaker wiring. Just unscrew the front speaker-mesh CC-wise, and you will be able to see four phillips screws

You're correct on the antenna booster, no antenna mast to go up and down on your MY, antenna in windshield.

[harborman]

Originally Posted by MPDano

Are you sure those a re stock speakers? I thought they all came with Blaupunkt Speakers (I stand corrected. I see a 928 part number on them. ITT?).

Anyways, you should be able to just follow the wire colors and what they go to. I ditched any stock fader control and wired it up so the stereo can handle this function.

All my speakers had ITT on them and quite sure stock originals.

[PC-85-928S]

anyone know how to check this relay?
Relay - Interference Noise Suppressor 85-95

[Fredfox]

I used a new sony with usb input. Eliminated the amps, did not need them. Only thing left was the fader knob. Bypassed that and now it sounds great.

[PC-85-928S]

did you run new wires directly to the speakers after the amp?
did you leave the amp in place?
did you unplug the constant 12v going to it or the switched or ground?

[MPDano]

did you run new wires directly to the speakers after the amp?

I ran new wires from Stereo to Amp, depending on where you put your Amp, I just reused or tapped into the existing wires that came from the old amp.

did you leave the amp in place?

I removed mine. No need to keep in place, but it doesn't matter since it's under a box.

did you unplug the constant 12v going to it or the switched or ground?

Any stereo I've worked with had a switched wire "and" and constant power wire. Switched turns the stereo off, but a constant will keep the presets, etc.

[PC-85-928S]

What I am thinking is this:
The original Montery SQR23 cass radio leaves the head area with 4 wires
RED
RED/WHITE STRIPE
BROWN
BROWN/WHTSTRIPE
These wires go to the driver's side Fader.
The Fader comes out with 8 wires going to the amp
The amp then feeds each speaker.
The new Madison CD127 has an amp built in.
So I was sending an amped signal into the stock 928 amp.
giving me static and popping

I think I need to take pre-amp lines from the back of the Madison to go into the fader, and then stock amp.
A pre amp cable is listed in the Madison manual, but it is no longer available.

[PC-85-928S]

this is the plug no longer avail
Blaupunkt's 8-634-494-218 Old 4-Channel Preamp Output Cable

[MPDano]

If you continue to use the stock wiring from the stock stereo, of course it's going to feed through the stock amp. Forget the Stock Amp, forget the Stock Fader.

Buy an Aftermarket amp, run your stereo wires to the amp, then amp to your speakers. I think in my previous posts, I have said i used the wires that come "out" to the speakers. This way, your only running new wires to your Amp.

Also and FYI, My Ford Expedition uses the Stock Head Unit which runs to the stock amp, which I have a Fosgate Amp connecting from the Stock Amp and I do not get any Pops or Static. I do get amplified hiss. Either you old Head unit or the Stock Amp is bad in your car.

[PC-85-928S]

PC-85-928S

Well that makes it easier to wire because the preamp output from the radio is not used. The four wires from the old radio are the positive and negative leads for the left and right side of the vehicle's audio system. They take the two channel (L & R) down to the fader, which makes the front and rear channels out of each side. This then goes to the amp. If you sent the preamp signal to the fader, then you would not hear hardly anything, even with the radio turned all the way up.

In this situation, I usually use the front left and right speaker outputs from the radio I am installing to connect to the two sets of speaker wires in the vehicle. This eliminated the need to rewire the whole system. However, it is possible that if the radio's fader gets turned all the way to the rear outputs, someone might mistakenly come to the conclusion that there is a problem with the system. You would use the socket just below the preamp socket, as shown on the diagram I sent you.

Sincerely,

Scott

Continental Imports
1219 S Main St
Gainesville FL 32601
(352) 377-6604
(352) 377-2218 fax
Continental Imports - Import Auto Service in Gainesville, Florida

[PC-85-928S]

Thanks to Scott from Continental Inports in Fla for helping me.

Dear PC-85-928S

I am sorry, my recommendation was made under a false assumption on my part. The Madison is quite old, and I assumed it was old enough to be, of the generation, of medium power, common ground compatible radios. After what you said I knew I was wrong, but looked up the information to make sure. The Madison CD127 uses a high power, "floating ground" output. The floating ground means that the negative side of the speaker output can not come into contact with any other negative speaker lead or the power ground. The 928 speaker wiring is drawn showing that the left side is completely isolated from the right side and power ground. There are a very small amount of 928s that this holds true enough that the radio would work as I described it. However, in the real world, some part of the system (and I think it is the fader) "leaks" back and forth. This makes the radio sound horrible, or cut out, as you described. If you used the balance control on the radio and moved it to the left only or right only, you would most likely find that the sound would clear up. But who wants to listen to one side only, any way.

Running new wires to the speakers would be the best idea anyway. The BQB80 amp is not a bad amp, just an underpowered amp. The "80" stands for the power output of the amp. This means that it is rated at four channels at twenty watts of power each. In reality, it can only provide about fifteen watts with low distortion. The Madison is rated at thirty watts per channel, so it is roughly twice as powerful as the BQB80. If you have not already figured this out, the easiest way to connect to the speakers directly, is to run wires from the radio down to the amp. All four of the speakers have individual plugs at the amp, and can be tapped into there.

Sincerely,

Scott

Continental Imports
1219 S Main St
Gainesville FL 32601
(352) 377-6604
(352) 377-2218 fax
Continental Imports - Import Auto Service in Gainesville, Florida