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Mon Aug 09, 2010 4:09 pm

I found this site that takes some of the mystery of of the plug (actually socket) sitting in your engine bay. http://www.nls.net/mp/volks/htm/plug.htm

If intact, it can be quite useful. I cobbled together this picture from that site. Maybe Captain Spalding can make it prettier.

Mon Aug 09, 2010 5:50 pm

The diagnostic wiring is in the wiring diagrams to an extent. It can be hard to read the colors because a lot of the wires are drawn in pretty short (or at least some of them are in the current flow diagram). I don't recall to what extent Captain Spalding worked to verify those wires. I tried to act as a second (maybe it was as a third or fourth) set of eyes on his wiring diagram project, but I don't remember looking at the diagnostic wires specifically in any detail. I remember finding some of them and noting that they matched the diagrams, but that is about as far as I remember going with that.

The 'computer' diagnostic system is generally agreed upon to be primarily a marketing item. Having said that, I will admit that it did do some pretty cool things and had the potential to do other cool diagnostic tests. The aforementioned site does a pretty good job of getting the basics so I will try not to repeat too much. Using the starter as a sort of compression tester was pretty neat in my opinion even if using an actual compression tester would yield more accurate results (I believe it was used primarily as a means of looking for one bad cylinder). Using the wiring as current shunts was also pretty neat in my opinion. Like the site says, at some point in 74 some, if not all, vw's got a tdc sensor that when used in conjunction with the #1 spark plug wire inductive sensor could give pretty accurate timing information for setting idle timing spot on. I'm talking about getting idle timing to a tenth of a degree spot on; try doing that with a timing light! You can read more about a later timing tool that vw implemented for buses here.

The diagnostic computer system did some other tests that aren't mentioned in discussions about the diagnostic socket. This is probably because they didn't have to do much with the socket itself. I don't remember all of the tests, but a lot of them were simple yes or no questions that the technician was supposed to look at something and say yes or no. Nothing of great value except for the reminding somebody to look at something part (I know I have a tendency to forget stuff when not reminded). I don't know if all of the diagnostic computers did this, but at least some of them had a special mirror set up that used the headlights to check the wheel alignment. I don't know how good of a job it actually did, but it was a cool concept.

I came across a manual for an earlier dealership diagnostic computer and for the life of me can't find it again to link it here. The only thing that I saw there that I thought should have been implemented with the diagnostic socket was an ignition oscilloscope. It used two inductive sensors (one on the #1 plug wire and the other on the center electrode wire from the coil) to create traces of the ignition system voltages that helped find ignition system faults like fauled plugs among other things and could pinpoint the fault to a specific cylinder. If I find the manual I will link it back here.

At one point I had considered trying to personally re-implement portions of the dealer diagnostic system, but that whole space time thing keeps getting the best of me.

Wed Aug 11, 2010 12:08 pm

I suppose where I was going this thread is explore possible "alternative" uses for the the diagnostic socket. Given the dozen or so stategic electrical points it just seems to be a convenient location to "plug into".

Some of the ideas I've seen so far are:

Hooking up a dwell/tack meter (Pin 13)
Remote start (Jumper + and Pin 50) I haven't tried this one
Trailer hook-up (don't no whether the wires could hold the current though)
Troubleshooting rear lighting gremlins (is it the switch or bulbs)

Any other ideas?

Wed Aug 11, 2010 9:34 pm

There really isn't anything stopping you from using the diagnostic socket to hook up to those things. None of the items that the original system tested are hard to implement individually; you just have to get a good jumper connection into the socket pins and the tool needed to use that test function - ie timing light for the plug wire inductor, dwell/tach for the coil connection, test light, etc. Like I said, reimplementing the diagnostic system or parts of it is on my list of things to do eventually (there are a lot of things on that list). One of the things I had considered for my implementation is using labview or a similar program to look at various voltage signals on a computer (basically allow you to build the complete system using modern equipment).

I am not sure on alternatives, but then again I hadn't really given a great deal of thought to it. I don't know how much current some of those test wires can handle. I seem to recall that some of them are pretty thin.

Mon Jan 03, 2011 7:36 am

On my 74, I want to remove the test socket as part of cleaning up the engine compartment. I don't want to assume that this will not break any circuits and I'm guessing I'm not the first one to do this. ANy help from those who have "gone" before me on this would be appreciated.

David

Mon Jan 03, 2011 12:07 pm

[quote="Semper_Dad"]I found this site that takes some of the mystery of of the plug (actually socket) sitting in your engine bay. [quote]

I have to admit my ignorance.

Is this block in all Thing vehicles? Or only the 1974 engine?

You see, I rescued a Thing that has no engine and I am still trying to get a handle on the correct one that should go in here, beyond comments like, "put a T1" or something similar.

I really need to know the differences and what would be worth putting in.

Plus the wiring in the Thing has been vandalized so I will be installing my own.

Mon Jan 03, 2011 7:08 pm

strelnik wrote: I have to admit my ignorance.

Is this block in all Thing vehicles? Or only the 1974 engine?

You see, I rescued a Thing that has no engine and I am still trying to get a handle on the correct one that should go in here, beyond comments like, "put a T1" or something similar.

I really need to know the differences and what would be worth putting in.

In the U.S., Things all had 1600cc dual port T1 engines. So yes, any 1600cc T1 dual port engine will fit with no problem. It can be from a bug, a 1971 bus, or a Ghia.

In Europe, the first 181s came with 1500cc single port engines, but with different gearings in the trans too, so it wouldn't be perfect for a US Thing. You can go with a bone stock 1600 DP, but also with any bigger engine (1776, 1915, ...) that are commonly found in the US.

The VW diagnose socket is not only found in Things, but also in Bugs, Buses, Ghias,... The VW dealerships at the time, had the machine and would plug this socket to their machine to diagnose. Like today with modern cars. I don't remember since what year this was introduced, but I believe the very early '70s.

Mon Jan 03, 2011 8:25 pm

dpalinsk wrote: On my 74, I want to remove the test socket as part of cleaning up the engine compartment. I don't want to assume that this will not break any circuits and I'm guessing I'm not the first one to do this. ANy help from those who have "gone" before me on this would be appreciated.

David

The test socket isn't necessary for anything, and unless someone used the wiring for something else it isn't doing anything useful. Some of the wiring is "hot" so at the least you should disconnect those at the source so you don't have powered wires going places for no reason.

Some of the diagnostic wiring can be useful though. The wires going form the battery to the socket can be useful if you want to run a tach or something through the firewall.

Mon Jan 03, 2011 9:05 pm

Pierre G wrote: strelnik wrote: I have to admit my ignorance.

Is this block in all Thing vehicles? Or only the 1974 engine?

You see, I rescued a Thing that has no engine and I am still trying to get a handle on the correct one that should go in here, beyond comments like, "put a T1" or something similar.

I really need to know the differences and what would be worth putting in.

In the U.S., Things all had 1600cc dual port T1 engines. So yes, any 1600cc T1 dual port engine will fit with no problem. It can be from a bug, a 1971 bus, or a Ghia.

In Europe, the first 181s came with 1500cc single port engines, but with different gearings in the trans too, so it wouldn't be perfect for a US Thing. You can go with a bone stock 1600 DP, but also with any bigger engine (1776, 1915, ...) that are commonly found in the US.

The VW diagnose socket is not only found in Things, but also in Bugs, Buses, Ghias,... The VW dealerships at the time, had the machine and would plug this socket to their machine to diagnose. Like today with modern cars. I don't remember since what year this was introduced, but I believe the very early '70s. Thanks, Piere, this was vewry helpful.

I can tell you about the 128 variations of the Citroen 2CV engines, but I am new to the VW world. This info was very useful.

Mon Jan 03, 2011 11:52 pm

strelnik wrote: Thanks, Piere, this was vewry helpful.

I can tell you about the 128 variations of the Citroen 2CV engines, but I am new to the VW world. This info was very useful.

You're welcome. Glad I could help. You have some good info here :

http://www.thesamba.com/vw/archives/info/engine_letters.php

A Thing engine shoud have a number starting with AH. But AE or modified AJ (to accept carbs) would work. And of course the replacement case AS too.
In Europe 1600cc dual port were mostly found on buses from 1971 to 1979, and beetles like 1302S and 1303S (super beetles). Their case numbers started with AD or AS.

Tue Jan 04, 2011 4:44 am

I beleive the '73 & '74 US imported thing had the engine designator of "AM"

Wed Mar 16, 2011 8:20 pm

Thread resurrection apologies. Finally found the link to the earlier diagnostic manual that I mentioned at the start of the discussion. If anyone is interested in reading through it, here it is: http://classicvw.org/gallery2/v/partsbook/Autoscan-Diagnostics/

Sun Aug 02, 2015 7:43 pm

I have a 71 fuel injected automatic square back. There is a long loose light green wire coming out from behind the test socket. Does anyone know what it should be hooked up to?

Mon Aug 03, 2015 6:20 pm

Is it white and green? If so, it goes to the #1 terminal on the coil, which is the negative terminal (same terminal the points go to).

Mon Aug 03, 2015 9:43 pm

Semper_Dad wrote: I suppose where I was going this thread is explore possible "alternative" uses for the the diagnostic socket. Given the dozen or so stategic electrical points it just seems to be a convenient location to "plug into".

Some of the ideas I've seen so far are:

Hooking up a dwell/tack meter (Pin 13)
Remote start (Jumper + and Pin 50) I haven't tried this one
Trailer hook-up (don't no whether the wires could hold the current though)
Troubleshooting rear lighting gremlins (is it the switch or bulbs)

Any other ideas?

In my '73 Bus, I used the diagnostic plug to install trailer lights. Because trailer lights are a pain, and need a converter, I prefer to use the powered type. They are similar to the converters, but the power for the trailer lights come through from the battery instead of the lighting circuits.

Anyway, I just soldered spade connectors to the converter's wires and plugged them into the appropriate holes in the diagnostic port.

I like the idea of using it as a remote start with the other terminals. I might give that a shot!

Tue Aug 04, 2015 5:10 pm

Is it possible to find a mating connector?
I see all kinds of good things you could do with this.

Sun Aug 09, 2015 4:16 pm

Besides the original diagnostic computers, which I think I have only ever seen parts for one in the last 14 years, I don't think they are available. At one point I was thinking about trying to figure out how to make my own, but that is pretty low on my priority list right now.