There has been a lot of talk about this subject. Here are some thoughts to help sort out the problem:

Symptoms: Wipers fail to park in the same position and often fail to park at all unless ignition is switched off. Wipers start to wipe again if the ignition is turned back on again after failing to park properly.

The system consists of a supply line that runs to the steering column windscreen wiper stalk switch. From here it runs to the controll relay no.377. The control relay then feeds the windscreen wiper motor. The motor has four connections. Earth, stop switch, continuous slow wipe supply and continuous fast wipe supply.

The stop switch connection is the key factor. In the correctly parked position, the stop switch signal from the motor has no volts on it when connected to a properly working relay. If you disconnect it from the relay, the motor stop switch, when the wipers are correctly parked, will show open circuit or possibly 0V with respect to the motor body which should be earthed.

When the motor is turning then the stop switch should show full volts as it connects in the motor to the supply for the fast or slow speed wipe. this is how the relay knows that it is not in the park position.

If the stop switch contact fails to become fully disconnected from the fast or slow wipe voltage lines then the motor will continue to turn as the relay does not recognise that the park position has been reached.

If the relay sticks then although the relay is trying to turn off, it still supplies power to the motor and hence the motor passes beyond the park position and the stop switch contact is re-energised telling the relay to keep powering the motor.

How do I check if its the motor switch or the relay that is at fault?

Beware of just measuring the voltage on the stop switch cable in the parked position. The result will depend on the impedance of your volt meter relative to the relay cct. Here is a more reliable method.

Remove the wiper motor. Its a simple job. Open bonnet. Remove nuts holding windscreen wipers and remove wipers. Remove drivers side scuttle cover (gently prise it away from the windscreen and bulkhead lip. Remove the three torx screws holding the mechanism and motor. Carefully rotate and remove the mechanism and motor as one assembly. Now separate the cable connector from the motor. Using a pin or thin screwdriver from the back of the connector, remove the stop switch cable (Green and Black) from the connector (not the motor side). Re assemble the connector without the stop switch cable connected. Place the motor and mechanism so that the motor can be run without jamming the mechanism or trapping anyones fingers. Connect a short length of cable to the removed stop switch cable. Now turn on the ignition and set the wiper to intermittent. The motor should start to turn (beware of trapping or jamming the mechanism on parts of the car or yourself) If it doesnt turn then try momentarily connecting the extended stop switch cable to the slow wipe supply (Green). Now here is the important bit. If the relay is working correctly, then the motor should stop as soon as you touch the extended stop switch cable to an earthed point. IF it doesnt and you are sure of a good earth then the relay is probably sticking. You can read how to clean this relay on other posts. If you can stop the motor instantly and at any position by earthing the stop switch extension cable then the likely fault is in the motor. Do not abandon hope?

Why might the switch operate incorrectly? One reason is that after a period of time a line of copper debris builds up on the rotating contact disc which means that the switch contact is always connected to the live. See picture.

Helpfully, my windscreen wiper motor cover plate was rivetted together which meant that by gently filing off the rivets, it was possible to gently prise off the cover plate and view the connection disc underneath (see photo). Wipe off any excess grease from the connection disc and gently clean the tracks and insulated section to ensure that tracking does not occur. I used scotchbrite. Spread a little of the remaining grease over the contact disc and replace the cover taking care not to damage the gasket. Now this is the best bit. Next to the old rivet positions are through holes that can be used to bolt the plate back in position. You can tap out the body of the casting (i think i used M5) or through bolt, or use pop rivets. There is one position next to the black plastic connector where you will need to drill out the rivot that you filed down and replace it with a pop rivot or bolt. I tapped all the holes so that I could easily dismantly the cover plate in the future. See photo. Re assemble the stop switch cable into the connector. Re connect the motor and re-assemble the motor and mechanism into the vehicle. Run the motor and check that the spindles now stop in the correct position on a reliable basis. Re fit the front scuttle cover and windscreen wipers, checking that in fast mode they do not strike the edge of the windscreen.

I must emphasise that the above represents my own long search into the wild windscreen parking problem and my own solution. As with all disclaimers, the above is merely a guide to what I did and you should ensure that you are happy that any instructions are complete, accurate, safe and not likely to damage your vehicle or its components.

The switch fault can be intermittent and depends on a number of factors including the number of times the wipers have been used, temperature, wiper load (dry or wet) and probably others.

For those who are interested:

Motor connections: Brown earth, green/black stop switch, green slow wipe, green/yellow fast wipe

Relay connections (please check): Earth 31, Stop switch 31b, slow wipe to motor st1, fast wipe to motor st2, intermittent wipe supply to relay from wash wipe switch 1, slow wipe supply to relay from wash wipe switch 53, fast wipe supply to relay from wash wipe switch 53b, washer wipe supply to relay from wash wipe switch 53c, Intermittent speed resistor POT, Relay supply probably from F24 13.

Total job time about 2.5 hrs. Total cost 5 screws. Satisfaction rating of having windscreen wipers working properly again after 4 years 10/10.

Hope this helps.

wiper motor photos.pdf

Edited 4 April, 201214 yr by blackwood_man

many thanks....