VW Dealership Diagnostic Plug Block Port Socket

[AlmostHeavenWV_VW]

TL;DR
-The diagnostic plug began in early 1970s and was used by VW dealership service centers to 'diagnose' and check various parameters of the engine and electrics using a special computer (pictured above)
-No one has a VW diagnostic computer anymore, but the diagnostic plug on early-to-mid 70s ACVWs can still be useful, actually (if the wiring isn't all hacked up by a previous owner)
-It connects to approximately 19 items directly. Some are useful even without the VW diagnostic computer, some are not.
-The remainder of the plug terminals are sort of a mystery. Could be additional 'testing' circuits for the old VW diagnostic computer to use to 'assess' or 'calculate' additional things, but the wiring diagrams only talk about what is connected directly to the plug block in the car. No diagrams (AFAIK) exist which explain/outline this diagnostic system from the computer side of the plug.

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Pictures of the plug in the car

Pictures of the computer end of the plug

I've been doing some research on whether or not the old VW Diagnostic plug in my beetle is useful in any sort of way. It's not that I dislike it being present or that it has caused any issues, but when I discovered that I can tap a 12v power source and a good solid ground out of it, I wondered.......

What all does that thing connect to?

So onwards into learning and adventure we go!![/i]

Resources:

SpeedyJim
http://www.speedyjim.net/htm/plug.htm

Samba search with lots of short, fragmented discussions:
https://www.thesamba.com/vw/forum/search.php?searc...=titleonly

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When did this port show up?

The Diagnostic port was introduced around the 1971 model year and continued at least until 1974 (VW just quietly seemed to do away with it in the later 70s).

What did it originally do?

It was used by the dealership to 'diagnose' many issues (some were more of 'estimations' that the VW computer would give rather than every 'diagnosis item' being from a separate sensor.)

Pictures of the VW Dealership set up

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So...many people ask:

[Zundfolge1432]

I leave them intact but I can’t tell you how many I’ve seen hacked for no better reason than to make things look cleaner. My 74 still has the plug and I worked around it when I installed the new tar boards. guess I’m a purist

[Glenn]

[vamram]

Great post, AlmostH, if for no reason other than laying out clearly what each connection does!

Have you actually tried any of the ports - say to check the voltage at your coil or to turn the starter over?
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[Eric&Barb]

Link

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[Gman73]

i wish my 79 had one. be cool to look at the fuel injection system on it.

[Gearfinger]

Was there, did that...

[busdaddy]

Impressive post, thanks for taking the time to round all that up, well done!
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[Meiang]

Here is the VW Diagnosis Punch Card Booklet.

[AlmostHeavenWV_VW]

[vamram]

[AlmostHeavenWV_VW]

[johnboy715]

My alternator light sometimes doesn't come
On at start up. Does the alt. Dash light wire connect or go through this unit? Wondering it could be the place it is shorting out? Any thoughts?

[bnam]

On the BMW2002faq forum, someone had built a box that plugged into the diagnostic port of a 2002 and did some basic measurements (tach, dwell, voltage, etc).

It should be possible to do something similar or even more sophisticated.

https://www.bmw2002faq.com/articles.html/technical...nual-r133/
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1971 1302LS Convertible (RHD) owned since '74
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1965 Karmann Ghia Coupe - under restoration
1966 Fiat 1500 Cabrio (with 1600 Twin cam)
1952 Citroen TA 11BL

[grandpa red]

Mine was intact and left it that way even though the original engine wiring has been changed.

I felt there were too many wires going to the port to remove it.
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'72 Beetle

[busdaddy]

[AlmostHeavenWV_VW]

Can you guys check tach/dwell, ignition voltage, generator ouput, VR input,system voltage & start the car without getting up from your chair?

I can with my control box for the VW Diagnostic Block

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1973 Standard Beetle
1600DP AK case
Solex 34PICT3 Carb
Bosch DVDA 205AJ Distributor

[vamram]

[73SlowBug]

[busdaddy]

Is that all?, I demand resistance values for every major light circuit as well as comparisons of voltage drops on grounds while cranking

Just kidding, Nice work!
_________________
Rust NEVER sleeps and stock never goes out of style.

Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
Stop dead photo links! Post your photos to The Samba Gallery!

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