A quick primer on reading the Porsche wiring diagrams

[Rich Sandor]

Hey guys, I thought I'd post this for Rennlist and Pelican members.

Since I've been doing a lot of wiring on my race car recently, I've pretty much reverse engineered the factory wiring harness, taken it apart piece by piece, and even disassembled the entire fusebox, in an effort to really understand everything.

The factory wiring diagrams are actually very simple in theory, but can be complete gibberish to the first time viewer.

The diagrams are found in the factory service manuals, which can be found by a simple google search. They are usually split up into several large PDF files, the one related to wiring is usually called Vol4_electrical.pdf, or something similar to that.

The wiring diagrams for the early cars ~1980-84 is a little different to the 1985.5 cars wiring diagrams. I am focusing on the 1985.5+ diagrams, since my cars have been 86, 87 and 91 models.

After you've found the diagrams, the next key step is to find the right pages that actually apply to your model year car. (since the wiring harnesses vary from year to year)

Let's say I have a 1987 model car, and I want to find the wiring diagram for it.

Page 97 (sheet 14) is the ABS, Airbag diagram for 1987 model 944s and 944 turbos.

Here is a GIF I have made of that page:
http://members.shaw.ca/rsandor5/ABS_87.gif

Notice the numbers across the top and the sides. The letters and number form a reference grid, so that you can follow the wires from page to page. This is the trickiest part of reading these diagrams.

The ABS/Airbag wiring (sheet 14) runs from 91 to 100. The next page/sheet would be 101 to 110, and so on.

You'll notice in the top left corner of the diagram (just below A and right of 92) there is a number K41, surrounded by a box. That number means that the wire goes to grid section K41. If you go back a few pages to where grid section 41 is, and look below the letter K, you'll find an A92 in a small box. This is how you follow wires from one page to the next.

If you see a DIAMOND with a number in it, it means that wire leads to that grid section, but it joins/welds with several other wires at that grid reference. So, if look at our ABS wiring sheet, and go to the bottom right, section J99, you will see a diamond with an H34 in it. If you then go to the sheet with the H34 grid section, and you look up that grid area, you will see a larger box with several grid references in it, one of which will be J99. That means several wires are leading to H34 and meet up/weld there. (usually brown, aka ground wires)

On the lines (wires) themselves, you'll see things like 0.5 WS/SW. This means that the wire is 0.5 thickness, and the wire is Weisse(white) with a Schwartz(black) stripe. (The second color is always the color of the stripe)

Be careful not to confuse GR (GRAY) with GN (GREEN) and WS(WHITE) with SW(BLACK)

The list of colors is as follows:
SW - schwartz - BLACK
WS - weisse - WHITE
RT - rot - RED
LI - lilac - PURPLE
GE - gelb - YELLOW
GR - grau - GRAY
GN - grun - GREEN
BL - blau - BLUE
BR - brun - BROWN (almost always a GROUND wire, leading to a MP or ground point)

0.5 is the smallest wire that you will find in the harness.
1.0 is slightly, but noticeably larger
1.5 is again bigger
2.0 is quite thick, and usually reserved for power supply wires
2.5, 4.0, 6.0, and larger wires are reserved for high power draw items such as headlights etc.

If you follow the wires, they will eventually lead to a PINOUT from either the fusebox, a relay, a switch, a light, or some other device.

If you again look at our ABS diagram and look at the ABS equipment on the left hand side, you'll see little circles with numbers - these are the PINOUTS from that box. Usually they are also stamped into the device itself. (but not always)

The other end of the wires might go to the fusebox - referred to as "CENTRAL ELECTRIC" by the diagrams. They will end at another pinout, but it will be something like G24 or O11 or D55. This refers to the pinouts underneath the fusebox.

The underside of the fusebox on my 1986 944 turbo looks like this: http://members.shaw.ca/rsandor5/fusebox_86.gif

So for example, if you look at our ABS diagram again, you'll see there is a 4.0 thick, RT (Red) wire going from pin7 at the ABS RELAY to pin D11 in the fusebox. If you look at my fusebox drawing, you'll see that block D has a white label on it, and pin 11 is in the first corner of the block.

If you go to your car, unscrew the corners of the fusebox and lift it up and out, you should be able to see this red wire going from the ABS relay to the corner of the white D block.

That is all for now, I hope that someone finds this useful!
Rich

[kfray]

Good write up, thanks for your effort.

[porschetub]

Your opening to this post summed it up,(great write-up by the way)for that reason I tend not to use them,but I guess what you have just done requires a good understanding of them regardless.
Knowledge of the wire colours is a great when tracing faults but I tend to stumble up on relays and curcuits @ times.

[Eric_Oz_S2]

Good summary. On the wiring diagrams i have looked at black is BK, etc. This is for the 88 on diagrams, perhaps the early cars are coded in German?

It is also worth noting that the terminal numbers used are based on the DIN 72552 convention. This is useful in determining battery (term 30) or ignition switched (term 15) supplies for example.

DIN 72552 - Wikipedia, the free encyclopedia

[John_AZ]

Thanks Rich & Eric,

I printed and put in my WSM

John

[944 Ecology]

You can also read this, which is pretty much comprehensive on the subject...

http://www.thesamba.com/vw/archives/info/wiring/Understanding_Euro_Wiring_Diagrams_Motor_Magazine_ April_2003.pdf

[John_AZ]

Read, printed & bookmarked.

Thanks George.

John

[seafeye]

If i can add some help to printing of large pictures or diagrams.
Here is the way to do this without having to scale the picture down so you can't read it. And in windows 7, xp, vista all you need is the factory paint program.

1.Open the image you’d like to print in Paint
2.Select: Print -> Page Setup (Vista and 7), or File -> Page Setup (in XP)
3.Under Scaling, select Fit to and change the setting to something like “2 by 2 page(s)”
4.Click OK
5.Print the image from Paint, and make sure to select “All Pages”
6. Now select your printer and print.
That’s it – you’re done. You can take any image and have Paint print it out on multiple sheets of paper. If you’d like, you can also adjust the page margins in the Page Setup. In any case, all that’s left is to trim the white border from the individual printed pages, break out the scotch tape, and go to town.

[Alan in AZ]

Or you could read this:

http://www.928-electrics.com/Docs1/Porsche%20928%20Electrics%200.85%20-%20WDP%20Only.pdf

Alan

[John_AZ]

Originally Posted by Alan in AZ

Or you could read this:

http://www.928-electrics.com/Docs1/Porsche%20928%20Electrics%200.85%20-%20WDP%20Only.pdf

Alan

Just Great!

Thanks,

John

[dlearl]

Originally Posted by Alan in AZ

Or you could read this:

http://www.928-electrics.com/Docs1/Porsche%20928%20Electrics%200.85%20-%20WDP%20Only.pdf

Alan

Sadly, link is broken. Did anyone archive it?

[944 Ecology]

You can find it here until Feb 18, 2025


https://drive.google.com/file/d/1aBQ3OcoqDY3m1f_y0C1dmy6qgjzuHKuS/view?usp=sharing

[Monkey Wrench]

a little warning for other readers.. I started looking at the above links, some went to a shaw site and it was a dead link , no big deal.. I had shaw webspace and mine was taken down by shaw too.. it was initially a part of my ISP's package, but shaw lkilled the websites I had created and I subsequently found a better IP and ditched Shaw. I dont think the saaw links did anything but maybe one a biut further down the page had gotten redirected to some bad website.

Somewhere just above here where Im writing now, in this thread, I clicked on something there and my computer started popping up "virus warnings" in window notifications..

I called out IT guys and he had a look , he said it wasn't; exactly a virus but I guess some corrupt website there there approved notifications and the website was generating these goofy virus warnings.. the warnings say you have a virus I think its actually a spoof not a virus.

it tried downloading a virus checker and the scan didn't find anything it could remove unless i got their paid version..bit of a scam there in itself...

I just came back in just to warn anyone else if they also see suspicious activity from any of the above links , then maybe we can have an administrator remove those posts..

it might be that a page just above expired and got redirected to some malicious website.

if any of the above linked websites look funny try not to click anything within them .


I had my IT guy remote in and he didn't find much , I deleted firefox or google chrome and installed it again.

it was a good thread and helpful in reading Porsche schematics.