Scirocco Register

Hi Guys

I thought I'd start a separate thread for this issue as it appears we have a few problems again with the boys car right

The front window-screen washer has stopped working. The lad thought it was the pump so he replaced it. It wasn't, that would be too easy.

So the fault diagnoses we've done so far is:

When you pull the lever you get 12v at the Red/Green termination at the pump end. So logically the pump should work.

I connected the main battery to the pump and it operates fine.

I checked the earths and they're good. I threw in another relay in case that was knackered but it's not that. Something somewhere is taking the 12v when connected to the pump? I'm completely stumped on this one. The MOT is due next week.

Please could someone shed some light on this issue?

Thank you

If you're getting 12V at the red/green terminal, the fault must be the pump itself or the return earth path.

Have you measured the resistance between the brown terminal on the pump and battery earth? It should be close to zero (a small fraction of the resistance measured through the pump).

Alternatively, measure the voltage between the brown pump terminal and battery earth when the washer switch is activated - it should be close to zero (a small fraction of 12V).

If either of these tests don't give the expected readings, then that indicates a poor earth

Hi GTI thanks again for coming back so soon. I measured the resistance and it was 0.1 so I know the earth is good. I did take the earth out of the connector and connected an earth fly lead from the battery straight to the pump but this made no difference.

I agree it all points to the pump but why does it work when I put 12v directly across the pump terminals from the battery? Logically it’s not making sense.

Is the 12v at the green/red wire the same when connected to the pump, as well as when disconnected? I'm just wondering whether there is a high resistance in the 12v path from the battery through the relay, so that the voltage drops massively as soon as significant current flows

That’s on my to check list tonight. As well as looking at the Wiper switch connections. I was thinking high resistance at the switch. I will report back our findings.

Ok so had a quick look at lunchtime. I have no voltage at the pump with it connected. I also swapped the back washer pump to the front for stamps but still nothing. I'm think this has something to do with the burnt out cable on my previous thread. I wonder if the cables have somewhat fused together? I will do a more in depth check tonight.

I would guess a very bad connection or frayed wire somewhere in the power line. With no load connected, it could easily "float" to 12V but then reduce dramatically once the pump load is connected.

I could do with an insulation resistance tester to check the lines. That would tell me if a cable was breaking down internally. I’ll keep plugging away.

In principle you can do a lot with a standard meter, by measuring resistance between the ends of each section of wiring, but for that, you need to know the start and end point of each section of wiring in the circuit and be able to connect the meter at both ends.

Insulation resistance is only really relevant where wires are shorting between each other, in which case both circuits would probably be energised simultaneously, or if shorting to earth, a fuse would blow.

So I put 12v down the switch cable and the pump worked, so the resistance must be the switch. Cleaned all contacts with a fibre glass pen which is excellent by the way. Contact cleaner for good measure and it all works a treat. MOT on Tuesday. Thanks GT for all you help.

Great news, good you managed to get or the bottom of it in time for the MOT