I think this is the diagram then, with the rectangular box containing 8 coming from fuse 22.

So there's a relay involved. V59 is the washer pump. Guessing the green violet wire is the one that's been replaced by a switched 12V from the G65 loom section.

Relay located in position 1A, apparently:

3 minutes ago, nta16 said:

Once you have the information kindly being given. -

This bit concerned me especially as your old battery just within what's in this thread seemed good and now you have evidence of previous wiring modification would rightly or wrongly put me on alert for other bits of different style and condition and care servicing, maintenance and repairs.

When you replaced the battery where the battery terminal clamps secure and clean (I'd clean the inside of the battery terminal clamps before fitting the new battery to be sure)?

I think I would be tempted to check for any voltage drops on positive and earth sides.

With the wiring diagram you should be able to tell how the pump works sounds like it might be a reverse polarity but I'm not an electrician or expert in anything at all, tho' I do have experience of s/h cars (often 20-50+ years old) and seeing a few bodges on them, particularly the wiring tho' of course those are much simpler electrics but the basics still apply, wires and connectors clean, secure and protected - and of course wired and installed correctly.

Yep, I cleaned the terminal clamps thoroughly with a wire brush, inside and out. 👍

Think I mentioned in the OP, we've not seen any evidence of other electrical issues apart from crap DAB reception, which has a fault on the antenna shorting to ground (not uncommon for the antenna base to fail from water ingress, I believe). I've not seen any other crappy wiring elsewhere. This one shocked me to see if I'm honest.

The green/white wire marked B622 on left of previous diagram, can be either floating (not connected to anything), 12V or 0V depending on stalk control position. Its origin is shown in the previous page of the diagram.

Edited 13 December, 202513 Dec by Breezy_Pete

A subtlety that has just 'unbaffled' me is that the power source  for fuse 22 is the rail B621, which itself can be switched up to 12V or down to 0V, thereby giving the reversability of the pump.

9 minutes ago, Breezy_Pete said:

I think this is the diagram then, with the rectangular box containing 8 coming from fuse 22.

So there's a relay involved. V59 is the washer pump. Guessing the green violet wire is the one that's been replaced by a switched 12V from the G65 loom section.

Brilliant, thanks for these diagrams. I'm not going to pretend I can read them properly, but I can definitely use them. Yep, the green/violet wire has been bypassed/replaced by a run of wire (bisected with a fuse piece), which runs from [I think] the A/C pressure sensor connector near the coolant tank, directly to the washer pump.

See above about the unusual configuration of fuse 22.

Whereabouts are you based?

2 minutes ago, Breezy_Pete said:

See above about the unusual configuration of fuse 22.

So that explains why I only get the pump operational in one direction with this daft wire in place, yeah? It doesn't have the ability to pass the 0v state? Just floating (nothing) or 12V, which makes it run 'normally', which you would expect to be the front windscreen. Is this correct? Apologies, I've no experience with electrics.

Just now, Breezy_Pete said:

Whereabouts are you based?

Yorkshire.

2 minutes ago, whitedot said:

So that explains why I only get the pump operational in one direction with this daft wire in place, yeah? It doesn't have the ability to pass the 0v state? Just floating (nothing) or 12V, which makes it run 'normally', which you would expect to be the front windscreen. Is this correct? Apologies, I've no experience with electrics.

Yep.

Wild guess that the relay has malfunctioned, and the subsequent bodgery has caused the observed behaviours and faults. Please also check fuse 31 (7.5 Amp rated), which feeds the coil of the washer relay (amongst other things),

1 minute ago, Breezy_Pete said:

Yep.

Wild guess that the relay has malfunctioned, and the subsequent bodgery has caused the observed behaviours and faults. Please also check fuse 31 (7.5 Amp rated), which feeds the coil of the washer relay (amongst other things),

Nice one, cheers. I believe the relays are difficult to get to due to their location (as you posted above), which could explain why this bodge has been carried out in the first place. Saves the cost and effort of swapping the relay, at the penalty of losing the rear washer. But passes an MOT...

Actually doesn't look that hard.

Check that other fuse first, might save you any such work.

7 minutes ago, Breezy_Pete said:

Check that other fuse first, might save you any such work.

Just checked it (Saturday night excitement in a head torch 🤣), not blown. Certainly worth a look though. Would the relay throw an OBD fault if bad?

Anyway the next steps I think would be:

1. Try to eliminate the dodgy wire and assuming the original wiring is still present, connect it back up to the pump as it should be.

2. Disconnect battery to reset BCM.

3. See what happens and/or if fault codes appear.

4. Potentially replace relay in position A1.

Edited 13 December, 202513 Dec by whitedot

2 minutes ago, whitedot said:

Would the relay throw an ODB fault if bad?

Unlikely I think, since it isn't controlled by any control modules directly, so it wouldn't be readily monitored as working/not working.

Other than step 2, which I doubt would do anything useful, your strategy seems sound.

I can't see that just reinstating the correct wiring will fix it, unless the blowing of fuse 22 was the original fault, and not found at the time of the bodgery.

1 minute ago, Breezy_Pete said:

Unlikely I think, since it isn't controlled by any control modules directly, so it wouldn't be readily monitored as working/not working.

Other than step 2, which I doubt would do anything useful, your strategy seems sound.

I can't see that just reinstating the correct wiring will fix it, unless the blowing of fuse 22 was the original fault, and not found at the time of the bodgery.

Yeah that was my first thought (fuse 22), but surely surely SHIRLEY anyone with the knowledge and ability to do this extra wiring and know it would work, would just check the fuses before doing so???

The fact that fuse 22 is sometimes a source of 12V, but also sometimes a 0V connection will be unexpected by anyone without access to the circuit diagrams.

1 hour ago, Breezy_Pete said:

The fact that fuse 22 is sometimes a source of 12V, but also sometimes a 0V connection will be unexpected by anyone without access to the circuit diagrams.

Touché. Thanks for your help on this, really appreciate it. 👍

So to update the thread and close this out (because it's really annoying when people don't do that 😉), I had an auto electrician out today to work on the car. After testing the original wiring and signals from the stalk were working as they should, he took out the extra wire and wired it back in to how it should be. And sure enough, the pump works absolutely fine in both directions. Rear washer instantly fully operational and rear wiper behaviour back to intermittent as expected. As suspected, the botch job on the pump wire was responsible for everything.

My theory is the previous owner of the car blew fuse 22 at some point - probably trying to overcome frozen screenwash - and struggled on with it, then when it came to MOT time, some garage has done that 'fix' to get the front washer working. Amazing really that rather than spending ten pence and thirty seconds replacing the fuse, they instead decided to go to all the effort of taking the wheel and arch liner off to butcher the original wiring. Crazy. Thanks again to @Breezy_Pete, it was great to be able to talk through this with the electrician with confidence.

As an aside, I've also had the aerial base replaced which has totally resolved the poor DAB reception and stopped the digital aerial short to ground fault. So if anyone else comes across this post and wants to know;

1. On the combi/estate, you need to remove the D and C pillar trims (which involves dismantling a lot of the boot surround) and take out the rear passenger overhead grab handles. Otherwise there's simply not enough room to get tools in to access the aerial without seriously risking creasing the headliner; you need the handles out before it can drop down enough. Online guides and videos for other VAG cars don't account for the steep upwards slope in the headliner on the Fabia estate, above the top of the boot hatch.

2. I used VAG part number 6C0035501Q which has a much larger footprint than the original (6C0035501A/N) and therefore better protection from water ingress. I believe the internal seals are better too. Fitment to the car is exactly the same, and I swapped over the existing screw-in M6 antenna.

PS: The fault code on the A/C low pressure hasn't come back yet either, only done one drive in the car but it would normally have shown up by now. We'll see if that was related.