wiring harness differences between B and C

[chastings]

What are the differences between the 311906021B and 021C wiring harnesses?
I have a 69 sb with a 311 906 021B ecu installed. It intermittently doesn't run right.
I've checked the grounds, changed the hoses, wiggled the wires... Cant figure it out
I'm gonna replace the wiring harness because its old and a lot of the wires have crunchy insulation.
I have a spare 311 906 021C ecu with a harness (also crunchy). I cant compare them well without removing the harness from the car.
I want to use the C harness as a template to make a new harness.
What are the differences?
Thanks in advance!
C

[KTPhil]

Before you leap into making a harness, please list the part numbers of the major FI components, including the ECU, TPS, and MPS. With prior owners swapping components and engines, we can't assume yours are original.

Then we can address what type of harness works for you (hopefully!)

Changes around that time included adding the cold start system, which may be a separate harness, or integrated into the main harness. Does your car have the cold start components?

[chastings]

Hi Phil!
The TPS is new and shiny and installed by VW last year.
No part number on it.
The TVS is old and wrong and not hooked up. It has 4 electrical spades on it. The one that WAS installed had 2. Neither one has a part number that I can see.
VW had the car off and on for 7 months, and it ran worse after they had it. Then I let a local guy have it; he replaced the air intake distributor with one that I had. He said the butterfly leaked around the shaft (I think he meant the valve the TVS is attached to.
When I got it back, the TVS wasn't attached electrically. It ran fine for 3 days, then bogged down again. Wont go over 27 mph.
What other part numbers should I check for?
It does NOT have cold start components installed that I can see. No huge valve by the IAD, no thermos switch in front, no relay
Thanks!

[KTPhil]

A '69 with a 5-pin TVS is a mixup of parts and years. It can be made to work, though.

Can you clarify?: TPS (throttle position switch) and TVS (throttle valve switch) are the same thing. Did you mean "shiny new MPS" (manifold pressure sensor)? That should definitely have a part number cast into it.

Photos of each component from all angles, especially the MPS, can also help identify things.

This may be a tough job to keep wire numbers and mixed up years working, but it can be done. You will have to be meticulous and probably make up a wiring template on a pegboard, or some other means of validating wiring end to end.

[chastings]

[chastings]

Pressure sensor (I think that's the name?) is 311906051B. THATS the one that VW installed last year.

And you want some of the pressure switch (the one kind of under the air clesner) too?

[KTPhil]

Some of your photos are not working...

You may have a mishmash of parts that won't play together well without a little reconfiguration.

That looks like a '68/'69 (A/B system) MPS, with a non-VW black plastic cover on it. This suggests they may have messed with the plug or adjustment. Could be good or bad.

I only see four pins on the TVS, not 5. The '69 system used PN 311-906-111B, a four-pin unit. Can you read that PN?

The pressure switch was only used on the A/B systems. Is it electrically connected to anything?

You might be able to see the ECU part number through the fender slots. That will be critical to know. Otherwise you will have to pull the two screws that hold it to the left side engine trunk wall. The base number is 311-906-021, with a suffix letter of B ('38/'69), C or D ('70/'71), or E ('72/'73). We just need the letter.

With some rewiring and adjustment, mixed parts can probably be made to work together. But we need to know what you have first.

Hopefully it turns out to be a consistent '69 system, and we can go from there.

[D/A/N]

[chastings]

They installed the silver thing.
Isnt it the fuel pressure sensor?
Its in the left side of the engine compartment. About 10 inches from the ECU.
And yes.

[chastings]

Sorry about the picture quality. My hands are still shaking from the flu.
Its dark out now, so I'll take a pic of the TVS first thing tm am.
The ECU that's installed is a "B"
I think the IAD is from a "D" or an "E". That's the one that was installed by a local shop because they said the butterfly leaked in the original. I kept the original. It seems fine to me?

I found the clymers today with troubleshooting procedures; I'm gonna do that this weekend

[D/A/N]

[Tram]

[KTPhil]

Yup, agreed the earliest TPSs were 2-pin. The 4-pin came later.

The 4-pin version added the contacts for the acceleration enrichment. Can he use the 4-pin and just wire up the pins that were the functional equivalent of the 2-pin TVS? Wasn't it just a closed throttle indicator? I've never taken a 2-pin apart to see.

[Tram]

[raygreenwood]

Also....it depends on the part #....and year of manufacture of the TPS...as to whether you can use a four or five pin TVS interchangeably.

All of the four and five pin used the same circuit board number. The enrichment function used an extra wiper on the inner circuit trace. Either from the start or after a certain point in time....even the four pin had the extra wiper....it just did not have a fifth pin to connect to it.

The four and five pin plugs are fulling interchangeable from the TVS. They snap right on and right off.

If it has the inner wiper track and its a fjve pin TVS you can simply use a five pin plug and insert just your four wires into the five pin plug in the right positions.....or if you want correct looks as well....you can snap the five pin plug unit off the TVS and snap on your four pin plug assembly.

When I get back in town in three days I can post some close up pictures of the requisite boards, board #'s and wiper tracks/arms.....and pictures of swapping plug assemblies from one to the other. Ray

[chastings]

I'm having a hard time putting the photos in today - it keeps showing an "X" without showing a thumbnail.

The part number on the throttle valve switch is
0 280 120 040
It has 4 pins

[chastings]

The pressure switch is old, dull silver, has a hose coming out of its inboard side, and I couldn't see whats in back. It was directly under the intake manifold pipes, right side of the engine bay

The pic didn't turn out. I'll try again in a few hours.

[chastings]

Tram; thanks for the troubleshooting pages!!
I THINK the ignition system is working? New plugs, wires, condenser, points... the coil tested good... ignition APPEARS to advance/retard when I mess with the distributor.
The ECU ends in "b", and has a two prong TVS wire. A local guy said that the IAD had a loose butterfly shaft and installed the one with the 4 prong TVS. I think he was wrong, but I was clutching at straws.
Thanks Tram!

[chastings]

Tram and KTPhil,
I can take apart the 2 pin TVS and send you a pic?

[chastings]

So I think part of MY problem is the interchangeability of the names.
I have the TPS/TVS thing straight now.
I've been looking at the Clymers... it doesn't have pix, dangit.
A bigger part of my problem is that SBs issue is intermittent. Its broken now, so I'm pretty happy.
How do I know if the IAD shaft really is loose? It seems fine. Any way to mic it? Or maybe spray some goo from one side into the interior?
Its kinda gross, but I could suck on it?
Again, clutching at straws.