Also in the Haynes manual, it says that reversing light is connected to ‘onboard supply control unit’ T6b45…

No idea where they would have got that from... There is no T6b45 - T6b only has 6 terminals!

In VW terminology, the fuse box in your photo (in the engine bay) is fuse box D (actually SD). All of the docs that I look at say that you should (for a manual gearbox) have a fuse in slot SD15 - which you obviously don't. Is there any chance it has been converted from auto to manual box?

One other fuse to check: SC35 (lower fuse panel under the dash).

 

Hey thanks heaps mate I will check SC35 tomorrow.
Here’s the page of the manual showing the connection to the SCU too for reference. Don’t think it was ever an auto though. Back to you when I’ve had a look at #35 (couldn’t attach the pic sorry )

 

 

Ah, Ok - T6b45 looks to be a Haynes typo. I can let you know more detail of the actual pin number on J519 later if you need it. Let us know what you find with SC35.

 

Much thanks man ! Investigations shows 10A fuse at #35 - tests fine. Weirdly (maybe it is, still trying to figure this beast out ) there’s 12V at the socket even with the keys out. Pic of the fuse box attached in case it’s helpful.

 

Hey I was talking to my stepson about your query re it once being an auto (he did the recent recon gearbox swap from the dead one when we bought it ) and he thinks it possibly could have been - he said the box he pulled out had wreckers pen marks on it. Don’t know if that helps any…

 

Have the reversing lights ever worked in the time that you've owned the van?

It seems there are significant electrical differences depending on whether it left the factory as an auto or a manual. I ~think~ that one of those is that if it's a manual, it has a fuse SD15, and if an auto, a fuse SC35 instead.

If you have any of the factory documents for the van (or can find a sticker in the footwell), you may be able to see from decoding the PRcodes whether it had an auto box originally.

I've never seen it written down in any of the VW literature, but I think one of the wiring differences is that with an auto, reverse gear status is signalled by the TCU in the box to the main body control module via CANbus, while in a manual it's just a simple switch on the box itself.

 

Thanks man I’ll have a dig around in the morning and see what I can find. The plug off the switch sure looks more like a network comms plug than a 12V switch plug. I’ll plug the ODB on to it over the weekend to see if I can glean anything from there maybe ?
Reversing lights have never worked though - we bought it cheap with a shot gearbox (no clutch or reverse gear ironically ) knowing we’d need to replace it. Now with the new box in everything works fine, drives great, just no reverse lights.

 

If you can find the PRcode list (maybe in the driver's footwell) then decoding it should show up something like this:

PRCode: G1C = 7-speed automatic transmission

That's for a 2010-onward van - in your case it will be a different code for the 6-speed auto trans fitted pre-2010.

If that's what you find, it may just be a matter of changing the coding - but that may need a fair bit of research.

 

Hey @triffic thanks for that - sent me down a rabbit hole of codes I never knew existed ! Though now it makes sense why we were looking for a KPE replacement gearbox. So, found the codes on a very distressed sticker under the drivers seat - and after much rabbit-holing found that it was originally a JUM - as you rightly guessed an auto box. (pic attached for reference in case I’m wrong)
OK so now we know as per your precious that Fuse15 won’t be involved and Sc35 is the one, which is all fine.
I wonder to try and short the switch connection again - I didn’t have the engine running, only ignition to ACC - wonder if that’s an issue ? Will test more over the weekend. Thanks heaps for your guidance thus far mate.

 

If it helps, the reverse wiring on J519 should be T6b pin 2 (supply from SC35), T6b pin 6 (connection to common point B520 in wiring harness) and T18a pin 10 (input from reversing light switch F4).

This might be a situation where you need a short subscription to erWin (you can even get a 1-hour subscription, I believe) just so that you can take a look at the wiring that would have been present from the factory on your actual vehicle.

 

Oh wow that almost lost me there - man this is a whole new beast, we’ve had Bugs, Kombi’s and T3’s up until this
I’ll get mack down the rabbit hole ! Thanks heaps man will go have a look at erWin too. Have a great weekend mate.