The 75 and ZT Owners Club Forums - Windscreen wipers gone berserk! MOT fail, HELP!!

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- - Windscreen wipers gone berserk! MOT fail, HELP!! (https://www.the75andztclub.co.uk/forum/showthread.php?t=316638)

Quote:

Originally Posted by slovcan (Post 2910887)

The OP said it happens when the wipers are set to automatic.

But he also said that it happens in all the other settings as well ...

Quote:

Originally Posted by MartinBrighton (Post 2910833)

As previously stated, the wipers go for 14/15 sweeps of the screen no matter which position the wiper stalk is placed in...

So I don't think it will be the rain sensor.

Martin; looking at the circuit diagram the BCU controls all wiper functions. There's a conventional switch inside the wiper motor assembly which closes when the blades reach the parked position. This signal is sent to the BCU. It's ignored if the stalk is set to keep the wipers running. However when the stalk is moved to switch off the wipers, the BCU detects this and begins to take notice of the state of the motor switch. When the blades next reach the parked position and the switch closes, the BCU cuts the power to the motor and the wipers stop.

Your mechanic was wise to re-seat the relays. Since that has not been successful I would urge you to ask him to re-seat the motor connector as I recommended in post no. 4. If there's a dirty connection here in the parking switch circuit, the BCU won't know when the blades have reached the parked position and won't remove the motor power supply.

Simon

When the blades next reach the parked position and the switch closes, the BCU cuts the power to the motor and the wipers stop.

Simon. I was under the impression that a contact opened and broke the circuit. A bit like the brake pad sensors but I could easily be barking up the wrong tree.---:laugh:

Quote:

Originally Posted by COLVERT (Post 2910947)

Simon. I was under the impression that a contact opened and broke the circuit.

One pole of the "parking switch" is connected to the earth side of the motor Jon. The other is an input to the BCU. I understand that the switch closes to earth a pin on the BCU. I've come across this technique many times on the 75/ZT and I appear to have verified it using my multimeter. :D

Simon

Quote:

Originally Posted by MartinBrighton (Post 2910833)

Hi there, many thanks to those who took the time to try to help with my wiper malfunction problem.
My mate had a look at the relays that control the wipers. As soon as either of the 2 relays controlling the wipers was taken out then the wipers immediately stopped. So in his view it is not the relays that are causing the problem.
One thing that I failed to mention in the original post is that the wipers continue to work even once key is taken out of the ignition.
As previously stated, the wipers go for 14/15 sweeps of the screen no matter which position the wiper stalk is placed in, and stop wherever they choose on the screen, thus the MOT failure.
There are seemingly no other electrical issues, alarm etc..,
Is it as simple as a new wiper motor? My mechanic mate isn't so sure of this because the wipers continue after keys out of ignition.
Any further advice gratefully received, Martin

Martin I have met this many times on my own 75s and on others I have never tracked down the cause but My thoughts are with the loom where it comes through the bulkhead at the fuse box. To date I have had success every time by changing the wiper stalk switch. this fix has lasted on every car I have done it to, bar one which i had to replace a second time.
It can be a nightmare as when they start for no reason in the middle of the night the car alarm goes off. Tourers are more prone to the problem than saloons. As I have said replacing the stalk switch has worked for me every time but I have never tracked down the problem.