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MG Midget and Sprite Technical - 3 position wiper switch

Hi help please , the previous owner had put a 2 speed wiper in my car. I've had the dashboard out and struggling with the wiring to the 3 way switch . It has 6 terminals 1,2,3/4,5/6,7,8. I have 3 wires , live and two that go the wiper that make it operate at two speeds . I have tried various combination with my multi meter and can't seem to get an off/on/on combination . Any ideas where to start . Is 1 the live feed for example ?
Mike Fairclough

Mike,

2-speed wipers have 5 terminals, the single speed has 3.

Has the previous owner fitted a 2-speed wiper motor, or just a switch?

Richard
Richard Wale

Yes it's definitely a. 2 speed wiper , if I put voltage directly to the wires it will work at two speeds . The Lucas switch is a 31788 if that helps
Mike Fairclough

Then it looks like it will need 5 wires, including the park circuit and the black earth to work!

The attached picture shows the connections required and the wire colours.

Looking at the wiring diagrams, the 2-speed motor appears to be fitted with a combined wiper/washer switch.

The earlier 8-pin switch only seems to be used on the single speed - that is what the wiring diagrams show, but what was actually fitted?

Richard Wale

The attached picture is from the BLMC Manual showing the last version of the 8-pin switch, but no connection to pin 3 on the motor, which would be 'fast'.

Richard Wale

Hi Mike,


There should be 4 wires to make it work with 2 speeds and park.


Green.........12 volt from fuse


Red/light green........ 1st speed



Brown and light/lighgt green......... park circuit.



The OE colour for 3nd speed is blue/lightgreen, but it depends what colour the PO fitted toi make it work.



With the switch in off pos u need continuity between the red/lt green and the brown light green fot it to park.

The green switches current between the red/lght green and 2nd speed wire.


Good luck
SR Smith 1

Thanks chaps think I am making some progress . Please see attached photo of connection block . There are 4 wires there ( you can just see the black earth that is to ground ) the PO extended the wires to the switch with different colours that doesn't help but I can trace them. So am I missing a wire , blue light green ? Parking wipers ! I have never had them on either of my midgets , just got good timing with the switch .

Mike Fairclough

You should be able to slide the connection off the motor and check that there is a switch in the block for the self parking it looks on the picture like the block is coming apart.
mark 1500 on the road Preston Lancs

Hi,


The pic seems to show the correct wiring for single speed operation, with all the OE colours present.


Can't see an extra wire to make it 2 speed tho?


To test the park switch functions cnnect a 12v bulb between the brown/light green and earth. Run the motor, the light should illuminate with every revolution.



All the round bodied wiper motors should self park and most of the older square bobied DR3A types did as well, tho they functioned in a different way.


If you find it parks the wrong side, the motor has probably been changed. It's simple swop to the park position by 180 degrees though.


Hope that helps.


Regards Steve
SR Smith 1

Ok thanks Steve , so discounting the toggle switch for a minute , if I apply power to the red and green the motor runs , and I attach the multi meter between brown / green and Earth I get about 6 volts that fluctuates a little with every revolution . Not sure how the park works ?
Mike Fairclough

this helped me get my head round how the park works when i had a problem when fitting a smartscreen wiper unit.

https://www.youtube.com/watch?v=1Ww5-pmiokc
mark 1500 on the road Preston Lancs

Ok, we're getting there.




Set your multimeter to show continuity.


With the swiitch in the off poisition work our which 2 terminals are joined.


Then work out whick of those terminals is joined to another in the first speed psition, the one thats common is the 1st spped, ie red/light green.


In other words this terminal connects to the brown,/light green in the off position and the green in 1st speed mode.


The green wire ic connected the 2nd speed terminal in the last position.


It's easier to work out than describe!


If you cant get a common circuit in the off position, you probably have a lighting switch and it'll never work unless you use an additional relay for the park.
SR Smith 1

Thanks Steve for taking the time with this .
So in the off position 1 and 2 are joined and nothing else
In the middle position 1 and 3/4 are joined and 2 goes off
In the bottom position 1, 3/4 and 7 are joined , 2 is still off .
Could quite follow your wiring instructions in last message , probably being a bit thick
Photo attached of the back of the switch , at this point I would be happy with 1 speed and parking facility

Mike Fairclough

The video helped me thanks Mark
Mike Fairclough

Presumably the motor needs 4 wires:

Black as an earth
A permanent live feed to operate the self park as it needs power even when the dashboard switch is off. This only switches off at the motor when the cam plate rotates to the park position
A low speed switched live
A high speed switched live.

But do the two speeds operate by having 2 different voltages? I had assumed that the higher speed feed energised an extra pair of field coil windings when switched on to give the faster speed?
Guyw

I found this diagram on the MiniForum (their website tried to give me a virus, but McAfee intercepted it!).

Have tidied it up and added the standard Lucas wire colours. It shows the 5 motor connections for 2-speed and the 4 switch connections (pins 2, 4, 6 & 8).

As in the video, the 'park' circuit has 2 functions:

Interrupts the ignition fed supply when the wiper blades are in the 'park' position

Applies an electrical 'brake' to the motor to prevent inertia overrun (applies 'earth' to both sides of the motor in the park position ONLY).

Richard

Richard Wale

As the drawing shows, the switch internally connects the park wire (brown/light green) to the 1st speed wire (red/light green) in the off position.


The motor continues to run until the park switch shorts to ground and the motor stops dead.


Try this Mike.


Green on 1 = 12v supply

Brown/light green on 2= park



red/light green on 3 = 1st speed



blue/light green on 7= 2nd speed.


Let us know if it works.
SR Smith 1

Thanks for persevering with this guys , I did as you suggested Steve . With the switch in the off position the wipers ran continuously , in the middle position they ran at what appears to be a lower speed . I noticed that it was a bit intermittent as I touched the terminals and when I looked the switch appeared to have been repaired in the past with small electrical screws. I took/ it fell apart and it appears I may need a new switch before going further . To be fair it does have a manufacture date of 1962 so it's done well. Question is what switch do I order as a replacement .
Photo of broken switch

Mike Fairclough

Sorry that didn't work Mike, it sounds as if that switch has a problem?



You need a 2 speed switch from an MGB..............


This one shoulkd do the job



http://www.moss-europe.co.uk/switch-windscreen-wipers-two-speed-wiper-bha4786.html?assoc=109366


Regards Steve



SR Smith 1

This thread was discussed between 01/07/2016 and 05/07/2016

MG Midget and Sprite Technical index

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