86 porsche 928s stereo wiring diagram?

I've been looking all over for something and can't find anything anywhere for a "s" model. there's 928 wiring info on this site, but it's for a non-amplified 928 models. The one I have here has the blaupunkt amp on the passenger side door sill and the fader knob on the drivers side sill and 8 speakers. Everything is still factory in the car but someone has been in there once before and there's butt connectors and a hacked mess behind the radio. I get no sound but everything turns on and gets power, so i want to track down where the speaker leads are and start from there and work my way back.

I found this one, which would probably work fine, but it's too small to read, lol. Something like this but legible is exactly what i need. Diagram

Pull the amp and use it's speaker outputs, probably all BROWN / red+ and brown- with 4 pairs. test to find each then wire directly back to a modern head unit.
Haven't done a 928 in about 15 years but that's what we used to do with 911s.
At the head unit you will have red = 12v+ constant.
Yellow or black = ACC.
Grey primary with something secondary e.g. = red illumination.
Brown Ground .
And one other find the other's first then via a meter or a test light connect this to the 12v+ constant. It should raise the antenna if it's the power type in the rear wing. If it's an amplified "bee sting" roof antenna, it switches that on.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

I tried popping the speakers at the amp, but got nothing on every lead i tried. There's only 4 outputs on the amp with 8 speakers. They are all browns (which I'm assuming negative)and then positives are blue, blu/wht, grn, grn/wht. This guy wants to keep it original, so I need to find where the problem is and then send out the damaged parts for repair. I've got the wiring at the dash all cleaned up and back to factory, but still no luck on getting sound or tracking the problem. I would rather use a diagram than start pulling door panels and such because I know what happens when you start to pull panels on a 25 year old car and this one is pretty mint. I'd rather avoid that if i can. Thanks for the reply though.

The easiest way would be to pull the carpet edge trim and follow the cables up to the rear speakers, right hand side because there should be little "other wiring" that side, check if the colour matches then back to the amp. You might also assume at this stage on a 24 year old car that all the speakers are blown and/or possibly wiring breaks to the front doors though obviously not the rear. By popping can I assume battery across speaker leads?
I know your customer wants original but even back then the Blaupunkt OEM was a POS! Any thing from a Montreal up to the ludicrously expensive Berlin with it's ridiculous stalk.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Never found a legible diagram, but talked the owner into replacing the radio. So here's what I did in case someone does a search for this particular car.

I found that the radio has a right and left output that go to the fader knob on the driver side. There it converts to a front/rear right/left output with a common ground for the left and right channels that go into the amp. Only 4 leads out on the amp and there's 8 speakers. The 2 door speakers are wired in series at 8ohms (4ohms per speaker) and the rear speakers are wired the same for each side. I left them in series and just ran wires down to the amp and bypassed it. Brown wires are all negative and then the blues and greens are positive. Left them at 8ohms per channel to see how it sounded, and it sounded great. No noticeable loss of volume. The 12v constant at the radio is just a small lead for memory because it gets it's power source from the ignition lead, so if you put a radio in, you're going to want to wire the constant to a different power source. I just ran a power lead with my speaker wires and used the constant at the amp for my radio.

Left out that you also need to power the antenna. It should be the black lead coming out of the antenna wiring and it needs 12v ignition. the wires at the back of the radio are: brown - ground, thick red - ignition, thin red - 12v constant (don't use), black from antenna - 12v in for power.