13.2 - Windscreen Wipers Park ( Peter Crosby / Dave Hurlston,  )

fig. 1 Fig. 2

This is a description of the wiper park function on the early XJ40s. I have to assume the later cars work the same way.

There are 3 modes for the wiper:

1. High and low speeds.
2. Single wipe.
3. Intermittent wipe.

There are 3 power connections to the wiper motor itself. One each for high and low speeds (primary power) and the other is for parking (parking power). Control and application of each is handled by the car's central microprocessor (ECU), which takes input from the wiper stalk switch, in conjunction with the wiper logic unit (WLU).

When you turn on high or low speed the wiper motor uses the primary power connections to supply power to either the low-speed or the high-speed motor windings. When you turn them off, the parking power comes into play. More about this below.

When you pull the stalk for a single wipe, you supply power to the motor through the primary power connection (low-speed) as long as you hold the stalk pulled toward you. When you release it, that connection is broken and the parking power again comes into play.

When you enable intermittent wipe, the ECU pulses the primary power via the WLU to move the wiper out of the park position, then releases that power and, again, the parking power engages. If you listen carefully, you can hear the primary power connection relay in the WLU click on and off. The interval for intermittent wipe is not, at least in the early cars, adjustable.

Now, how does the parking power work? This power goes through an undocumented inline fuse behind the passenger's side underscuttle. The fuse is rated at 5 amps. The wiring is such that power is only supplied to the park circuit when it is not supplied through the primary circuits. The power is applied through a switch (park switch) which is in the wiper motor gear box and rides against an adjustable cam plate. The position of the cam plate determines the park position of the wiper.


So.....

1. When you go from low speed or high speed to off, primary power is disconnected and parking power is applied to the park switch. With the contacts closed (non-park position of the wipers) the motor is run until the wiper reaches the park position and the switch opens, disconnecting power and stopping the wiper.

2. When you single wipe the wiper (pull the stalk to you and release it), power is applied through the primary power connection until you release the stalk. At that time, parking power is applied through the park switch until the wiper reaches the park position and the switch opens. Then the wiper stops.

3. When you use the intermittent mode, the ECU pulses the primary power relay in the WLU to move the wiper off the park position and close the park switch. Then primary power is disconnected and power is applied through the park switch until the wiper reaches the park position and the switch opens. Then the wiper stops.

Typical problems are:

A. Wiper stops immediately, wherever it is on the windshield, when primary power is disconnected.

This is usually caused by the inline fuse blowing (often because the wiper was stuck). If it has not blown then look for an open circuit between the fuse and the motor. If it blows repeatedly, look for a short in the wiring, a gummed up or bad wiper motor, or a bad park switch.

This can also be caused by a badly miss-adjusted park switch, such that the contacts in it are always open. Adjust the switch so that the contacts are closed when the wiper is not in the park position and open when it is.

B. Wiper parks, but in the wrong place.

This is usually caused by a bad or miss-adjusted park switch or the cam plate the switch rides against. The switch may not work correctly if it is loose such that the cam will not open and close the contacts. The cam plate may have shifted causing the wiper to stop in the wrong place; it can be re-positioned.

However, it might also be that the wiper itself is improperly installed on the motor output shaft. Check and adjust the switch and cam plate first. Then, if necessary, loosen the nut holding the wiper arm to the shaft, work the arm free from the conical shaft, position the blade on the windshield in the desired park position, and re-tighten the nut.

C. Wiper runs all the time.

The problem is that the park switch contacts are never opening. It is caused by a bad or miss-adjusted switch.

Note: pulling the in-line fuse out will allow you to manually park the wiper until you have the time to pull the top plate on the wiper motor and correct the problem.

If the wiper operation is erratic, and stops at different places on the windshield, the problem is often a faulty micro switch.

Access to the micro switch is easy. Picture 1 shows the wiper motor and the control box on the left off the motor. Picture is for a 1990 XJ40, Left Hand Drive.

Unclip the connector and move out of the way. Remove the 4 torx screws that hold the cover plate in place together. You will see the micro switch inside. Picture 2 shows the micro switch, The switch cover has been pried off for access to the contacts.

WARNING. There is 12 volts on the micro switch at all times. If you touch the switch contacts, the wiper may cycle, so be prepared. You may prefer to disconnect the battery ground before going any further.

The switch can often be cleaned, but if the contacts are really badly pitted, it should be replaced. Electronic stores are a source for a replacement.

To clean the switch, use contact cleaner and then a thin piece of cardboard. Draw the cardboard between the contacts while applying gentle pressure to close the contacts on the cardboard.

Test the wiper operation, and if OK, put everything back together.

The park switch is a rather standard microswitch and should be available from most electronic supply stores. Doug Bernard (dbernard@datecinc.com) offered the following part number and supplier information: Brand: OMRON Part#: V-16-1C24 (Second xref number is 3189RA2) It can also be purchased from the Jaguar dealer or parts supplier using the part # JLM-011332 (thanks Don Czapski czapski@sprynet.com) and costs less than $20 (USA).