A Quick Word About.....The Mysteries Of The DS Wiper Motor.

Over the years I've seen lots of posts on Facebook and other forums about problems with DS wiper motors. Posts like this....

And this...... 

And this.....

This one (drawing power with motor off):

And how about this?

These examples relate to 1968 cars that have the same wiper motor, and wiper motor switch as my car. Heat seems to be a theme. Heat is bad. Especially if the motor is meant to be turned off because heat can cause a fire..... The other theme seems to be confusion over how to wire the wiper motor up - what connections go where. And why. 

 

A wiring/ colour coding problem I discovered when I rebult my wiper motor reminded me of these other problems and I decided to get to the bottom of my wiper motor circuitry once and for all.

Just to be clear, this is about a Bosch wiper motor from a mid/ late 1960s car, controlled by a knob on the dashboard. I don't know how much of this will be relevant to later cars (October 1969 onwards) that have the wipers controlled by a stalk on the dash. The two unit's are easy to distinguish. Later  - post October 1969 - cars have FOUR cables and solder points on the gear head.

Later four wire motor (photo credit: Mathieu Dutre)

My car, with a two-speed mechanism has THREE contact points and solder terminals.

Two speed motor with three solder points

 Cars from the early 60s had one speed motors with just TWO contact points.

One speed motor with two solder points (photo by PaulE)

These earlier one speed wipers were controlled by a simple 'pull/ push', 'on/ off' knob.

Pull/ push wiper switch for one speed wipers

When the two speed wipers (like mine) were introduced, the knob looked similar, but rotated between 'off' slow' and 'fast'. The head of the knob has an arrow on it so you can tell what speed position its in. This photo shows 'off'.

Twisting switch for two speed wipers - note arrow

I recently dismantled and rebuilt my wiper motor and studied how it was wired. You can read about that HERE. I'm going to walk through all the components and connections. Then I'm going to propose  some wiring diagrams showing how the circuits fit together. Then  - based on that - I'm going to describe how it seems to work.

Power supply to the Switch and Wiper Motor

From the battery, the 12V supply goes into the loom and emerges at a fuse (the yellow colour-coded fuse)  - which just happens to be over by the wiper motor.

Fuse box under the wiper motor

From there, the supply goes back into the loom and splits into two feeds.  Once feed goes to the wiper switch on the dashboard.

 

It's worth pointing out that there is another similar arrow-headed switch on the dashboard - the switch for the parking lights (off, right and left). If you are groping around with wiring behind a part-dismantled dash, it's easy to get these muddled. The wiper motor switch has THREE pins on the back.

Wiper switch has THREE pins

The power from the loom connects to the green colour coded terminal of the wiper switch. That is power 'in' to the switch.

'Green' is power in to the switch

The other two terminals (red and blue) are power out of the switch.

'Red' and 'blue' are power from the switch to the wiper motor

The wires that connect to red and blue go back in to the loom and emerge in the engine bay at the motor and still have red and blue tags. The other branch of supply from the fuse goes directly to the wiper motor area as the black tagged contact.

The three wiper motor connections coming from the loom

All three of these wires are for carrying supply to the wiper motor. Remember that the black-tagged supply does not pass through the wiper switch or the cars ignition switch. Other than the fuse blowing - It's permanently live.

 

So what you find coming from your loom at your wiper motor is:

• a black tagged wire (permanent live feed)
• a blue tagged wire (switched feed from the dashboard switch)
• a red tagged wire (switched feed from the dashboard switch)
  

External wiper motor connections

On the alloy gear housing of the motor is a cream or off white platic insulating strip with three solder connections points. The alloy gear housing also has an 'eye' hole through which these three wires pass. It's just a cable tidy really but serves as a useful reference point. I'm going to call the solder point furthest from the eye 'solder point A'. I'm going to call the middle solder point 'solder point B' and the solder point nearest to the eye..............'solder point C'.

 

Arbitrary labelling of the solder points

Each of these solder points has a short colour-coded wire with a male bullet connector on it.

These connect to the three equivalent coloured wires on coming out of the loom.

Three power supplies to the wiper motor

Two wires emerge from a hole in the gear housing near where it joins the main motor body.

There is a thick wire in a brown woven sleeve. This also joins to solder point B - the middle solder point.

Note that the brown sleeved wire is a thick wire

The other wire is a thin wire in a white plastic sleeve. This joins to soder point A - the one furthest from the eye hole.

Note that the white sleeved wire is a thin wire

 

Inside the Gear Casing

With the motor taken apart we can see what is going on on the other side of that cream plastic insulating strip. Solder points 'B' and 'C' have two contacts that extend into the casing body. The end of solder point 'A' is just bent over to secure it within the cream plastic strip.

The wiper motor gear wheel is within the gear casing lid. It's made of nylon or some similar material, but has a conductive metal disc on it's surface. When the gear casing lid is fitted, the two contacts described above both contact the metal disk as the gear wheel rotates. Note that the disc has a segment cut out around it's outer circumference.

 

Wiper Motor Body - Internal connections

I'm now going to follow the two wires from the outside of the cream plastic insulating strip back into the motor itself.

The thick wire in the brown woven sleeve is one end of a 'stator' winding fixed to the inside of the motor body.

 

The thin wire in the white plastic sleeve also goes to the same 'stator' winding core (arrowed) - fixed to the inside of the motor body. 

The two wires are wound around the same core

Crucially, and although this winding is part of the same overall winding as that of the thick wire  - the two are insulated from each other. 

 

In this next photo of the other end of the motor body, you can clearly see how these two (thick and thin) wires come from the same core.

The other end of the thick wire goes to one of the armature brushes at the other end of the motor body. I'm going to call this 'brush 1'.

The other end of the thin wire goes to the other brush. Yep:  'brush 2'.

As you might expect for a motor, there is another stator winding opposite the one(s) just described above. This is made of thick wire. At the gear casing end of the motor body, one bare end of the wire is fixed to the steel casing somehow - possibly soldered?

One end is fixed to the casing

The other end of this winding joins 'brush 2' along with the thin wire.

That's just about it: all the wires and their end points are accounted-for. Having described the connectons on the motor brushes, I'm not going to bother describing the armature - the part that turns - as it can't really be fitted or connected wrongly.

 

So what's going on? How does the wiper motor actually work?

Circuit Diagram(s)

This is the diagram for a mid/ late 1960s two speed wiper motor found in the repair manuals. The Citroen workshop manuals show how the motors are wired into the cars loom, but don't show the detail of connections inside the switch and wiring inside ther wiper motor.

Note  connections 'Bl10' and 'R11' on the wiper switch (30)

 In fact even what the manuals do show can include errors with colour coding...

Incorrect: note how 'R11' at the wiper switch (42) has become 'Bl11'........

There is a variant diagram as, for a few short months Citroen briefly fitted an additional flying earth lead to the outside of the casing but in all other respects the circuits are the same.

Short-lived additional flying earth lead (49)

Someone also posted another snippet of a circuit diagram relevant to 1967/68 wiper motors, but I don't where it originated.

These kinds of diagrams are helpful for showing connections of the loom, but don't explain how/ why the wiper motor works. To me, the most useful thing about the diagram above is that it shows that it's the 'Bl' (blue) wire that is part of the 'park' mechanism - rather than the 'R' (red) wire. That narrows it down a bit!

 

Based on my photos and the wiring described above, I produced my own circuit diagrams and I'll tell you how I think it operates. I'm not an auto-electrician and these diagrams are intended to show the 'active circuits' - the circuits doing the work in the given scenarios. I have greyed-out wires and connections not playing a key role. the diagrams are about current flow - and so motor operation - though this is not to say that electical testing will not show continuity between some points.

 

Basic Wiring Diagram

This is the 'basic' diagram that shows all of the wiring.

Note how the thick wire coil coming from solder point 'B' goes from 'Brush 1' and through the armature to reach 'Brush 2' and the second, thick-wound coil. Note how the thin wire coil bypasses 'Brush 1'.

 

Slow speed - first knob position
In 'slow' mode, the contacts inside the switch provide power to both the red and blue contacts and so both the red and blue inputs to the wiper motor. Power goes into the motor directly via the wires connected to the solder points (points 'A' and 'B'). The sweeper brushes on the gear inside the gear case play no role.

In this switch position power flows through the winding made of thicker wire and the winding made of thin wire. The circuit of the thin wire is earthed via 'Brush 2' and so links to the other, thick wire, stator winding and earth. As such, all the stator windings are activated. In bench tests, the current draw on a motor was about 4.4 amps.

Switch in 'slow' position: current draw was about 4.4 amps.

Fast Speed - Second Knob Position
In 'fast' mode, the contacts inside the switch only provide power to the blue contact of the switch, and so only to the blue input on the wiper motor. Power goes into the motor directly via the wire connected to the solder point 'B'. The sweeper brushes on the gear inside the gear case play no role.

 In this switch position there is no power to, and through, the stator winding made of thin wire. In bench tests the current draw on the motor reduced to about 3.0 amps. With the stator field reduced, the result is that the armature is able to turn faster.

Switch in 'fast' position - current draw is now only about 3.0 amps

The principle at play here is apparently called "field weakening". Here is something I stole from a Google search:

 

"Field weakening is a motor control technique that allows the motor to operate at speeds above its rated speed by weakening the magnetic field in the motor’s stator. By reducing the magnetic field strength, the back electromotive force (EMF) decreases, enabling the motor to rotate at higher speeds."

So there you are....

'Off' Position - During Parking of the Motor

If the wipers have been running, when the switch is put to the 'off' position, the wipers continue to run momentarily. Even though no current is flowing through the dash switch, the motor has an independent permanent supply via the black-tagged contact (solder point 'C'). 

During the 'parking' stage, the sweeper brushes inside the gear casing - and the metal plate on the gear wheel - play a crucial role. The permanent supply to the motor via solder point 'C' leads to a sweeper brush inside the gear casing (the one with the nipple in the photo below). The sweeper brush contacts the metal disc on the gear wheel as it rotates.

As well as there being a direct wire-to-wire contact between solder point 'B' and the first thick wire coil, solder point 'B' also has a sweeper arm that contacts the metal disc on the gear wheel as it rotates.

When the dash switch is initially put in the 'off position', the motor continues to turn because power is able to enter the motor via the brush under solder point 'C', travel through the disc on the gear wheel........

Note the cut out segment in the outer track

.......go back out of the motor via the sweeper brush on solder point 'B' and, from there pick up on the point 'B' circuit -  the thick wire circuit to the windings and armature.

Off Position - Motor 'Parked'

Although, with the switch in the 'off' position the motor initially runs on, this running of the motor - and so rotation of the gear wheel - ultimately cuts off the power supply to the motor. 

The outer circumference of the disc on the gear wheel has a segment cut out. When the rotation of the gear wheel is such that the brush under solder point 'C' is over the non-conducting segment of the metal disc, power is no longer able to flow through the disc and back up and out via the other sweeper attached under point 'B'.

Although there is a permanent power feed to point 'C' on the outside of the motor, it cannot access the circutry associated with point 'B' and so the motor stops turning.

When the wiper switch on the dashboard is next switched either the 'slow' or 'fast' speed positions, power flows directly through solder point 'B' (or points 'A' and 'B' together) and so bypasses the 'parked' metal disc. The motor is able to turn again.

PROBLEM SOLVING

So what might account for the symptoms described in the Facebook mesages at the beginning of this post? 

 

Wiper Motor Switch Only Works with The Ignition On

The supply from the battery goes directly to the fuse. From the fuse, one branch of the supply  goes directly to the motor and the other branch goes to the wiper switch on the dashboard. It doesn't first go through the ignition circuit. If the ignition is controlling the wiper switch, then the supply into the wiper switch must (wrongly) be coming from a 'switched' source - meaning incorrect wiring or the wrong wire connected behind the dash.

 

Motor Get Hot Even With The Switch In The Off Position

If the motor is getting hot, this implies there is current flowing through one of the windings. Any current going through solder point 'B' passes through both thick wire windings and the armature, so there would be motor rotation. It's basically the 'fast' mode setting.

Any current passing through solder point 'A'  but not solder points 'B' or 'C' would flow through the thin wire winding and the second thick wire winding before going to earth. Crucially it would not flow through the brushes and armature and so there is no motor movement. To me, this  false 'off' scenario has the potential to make the windings hot. 

If this heating up is occuring with the switch in the 'off' postion, then it implies that the supply causing the heat is bypassing the switch. This in turn implies that the black-tagged, permanently live feed coming from the loom at the motor has been connected to the short red-tagged wire connected to solder point 'A' at the motor, instead of the wire connected to solder point 'C'. Remember that in this scenario the thin, and one thick, winding are permanently connected to a power supply and earth. Like this:

A wiring error like this may account for a hot motor when 'off'

 

Motor Gets Hot When Switched Off, But Otherwise Works As Intended

I couldn't work this one out. if the heat (when off) is attributable to putting the intended solder point 'C' wire to solder point 'A', as above, and if the wiper switch is assumed to be wired up correctly, then the two wires from the switch can only go to solder points 'B' and 'C'.

As these two contacts ('B' and 'C') are connected through the park function, then putting the wiper switch in either 'slow' or 'fast' would indeed cause the wiper motor to operate. However I think the two speeds would be the same - both 'slow' - because the thin coil winding is permamently live?

 

Switch Works - But In The Opposite Direction

This one I really couldn't work out. The inference is that the expected 'fast' switch position actually equates to 'parked' and the 'parked' position equates to 'fast'. 

 

The wiper switch has one power feed to it and two sources of power coming out - depending on the switch position. In it's intended 'off' position, no current flows from the switch - so I can't see how this can equate to a fast wiper speed. 

Other Problems

There is a joker in the pack..... In this post I have described the middle solder point on the motor  (solder point 'B') as the one having a blue-tagged connection. Because of how the swiper switch works (and how the windings have to work together to produce 'slow' and 'fast' speeds), I feel that is correct. And it matches one of the workshop wiring diagrams earlier in this post.

However if you've read my previous post HERE - about my wiper motor rebuild - you will see that on my motor, and the spare one I obtained, the middle wire had the red tag. The blue tag was on the wire connected to solder point 'C'.

These coloured tags are in the wrong order...

Until my recent motor build, a lot of my thinking - and my contribution to discussions - was based on this (mis) understanding.....Ooops! But I'm not alone. here's another wired that same way:

Red tagged wire is in the middle position..... (photo credit Maac95)

Right. Enough excuses. If you correctly wire up your wiper switch, but follow this incorrect wiring at the motor (so blue to 'wrong blue', and red to 'wrong red'), what do you get? Well....in the 'slow wipe' position, the motor runs normally.

 

However iIn the 'fast wipe' switch position, the motor turns momentarily until the 'park' position is hit. It then stops but is still drawing a current - so will probably get hot..... 

I tested this theory. I incorrectly connected the motor to the switch as described. Slow speed worked, but not fast - although the motor continued to draw about 2 amps. I didn't wait to see if the motor got hot - but I'm sure it would have done. 

So how come  - if my tags are muddled - the motor on my car worked fine and had two speeds? Was there a manufacturing error somewhere at some time that Citroen addressed simply by swapping over connections behind the dash? It's possible, but now that my dash and original loom are out, I'll never know how it was wired when it was originally working.

 

It's an easy fix though: I simply swapped the tags on the wires over!