Wiper motor wiring

A popular modification for early Sprites and Midgets is to replace the single speed wiper motor with a dual speed motor from a later model car. While it’s relatively easy to wire up a switch for the two speeds, getting the wiper motor to auto park when the switch is turned off can be a little more tricky.

These notes document how I wired up a 2 speed wiper motor as found in a 1971 US specification MG Midget. As wiring can and does vary between models, as well as previous owner modifications, any modifications you attempt to make to the wiring of your car based on these notes are entirely at your own risk. Beware, Electrical faults can cause fires.

I haven’t dismantled a wiper motor, so I don’t know for sure how the motor is wired up internally, but several hours of studying a worksop manual and the wiring diagram of a 1971 US spec. Midget with 2 speed wipers and a lot of trial and error eventually revealed the secret of the wiper motor auto park circuit. We are now talking real Lucas Prince of Darkness stuff here!

What I found was that the auto park wire on the wiper motor could only be connected when the slow and fast speed wires were off. When you supplied power to either slow or fast, you had to disconnect the auto park lead otherwise there was a certain point in the wiper motors cycle where the auto park lead temporarily shorted to ground. I would imagine that if you left it permanently connected the auto park switch/mechanism inside the wiper motor would eventually destroy itself.

Using a cheap OFF/ON/ON toggle switch and and a relay (Hella 3057 12V 40/15A) it’s relatively simple to get both wiper speeds and the wiper auto park to work. The switch I use looks reasonably close in appearance to the original Lucas dashboard switches. I didn’t have a spare headlight switch to try with this circuit so sorry folks, I can’t tell you if it would work or not. (If anyone does try this let me know and I’ll update these notes accordingly.)

I solder all of my connections, covering the joints with heat shrink spaghetti, then for neatness finish by binding up the wiring with electrical tape. I have a pet hate of those quick crimp wire connectors as they can corrode and cause poor electrical connections.

On first inspection this circuit looks like it can’t work, but does as you’ll see in my explain a little later.

wiperdiagram2

I’ve tried to include the wire colours that appear in the workshop manual wiring diagram, if you can get part of the original wiring loom with the wiper motor, this makes it easier.

RLG – Red Light Green, NLG – Brown Light Green, ULG – Blue Light Green, GK – Green Pink.

Also note, I haven’t drawn the Wiper Motor connections in the above diagram as they actually appear on the motor (as a double row), but instead to make the above diagram easier to read.

The pin connections on the Wiper Motor are as follows:

wiperpins 1 – Earth
2 – Auto Park switch
3 – Fast
4 РAuto Park  +ve supply
5 – Slow

HOW DOES IT WORK

Flicking the toggle switch to the first position (slow operation), power is applied to the relay, closing the contact and supplying power to pin 5 on the wiper motor (via pin 87 and 30 on the relay). The Auto Park connection on the Wiper Motor (pin 2) is not connected to anything while the relay is energised.

Flicking the toggle switch to the second position (fast operation), power is supplied directly to pin 3 on the Wiper Motor. At this point you might expect the relay to turn off, but in fact the relay remains turned on by current leaking back out of pin 5 (slow) of the wiper motor (via pin 30 and 87 of the relay). The Auto Park connection on the Wiper Motor (pin 2) is not connected to anything while the relay remains energised.

Flcking the switch to off, causes the relay to turn off, this connects pin 2 of the Wiper Motor to pin 5 of the Wiper Motor (via pin 87a and 30 of the relay). What I think happens here is that power is connected to pin 4 of the Wiper Motor, this must be internally connected to pin 2 via a switch, which allows us to continue to supply power to the slow pin 5 of the motor until it reaches the park position when pin 2 turns itself off.

POSSIBLE ENHANCEMENTS

Although I haven’t done this yet, one obvious enhancement that can be easily made to this circuit is the addition of intermittent wiper operation.

The simplest way would be to connect a momentary push button switch from the +ve supply to the slow wire of the toggle switch (or pin 86, or 87 of the relay). Just press the button for a single sweep of the wiper blades.

Taking this one step further you could add a simple electronic timer circuit to turn the relay on at say 10 to 15 second intervals. You would probably want to replace the toggle switch with a rotary switch that had multiple positions so you could then setup the switch  to have: Off РIntermittent РSlow РFast.

This article may be reproduced for non-commercial purposes only, and full credit given to the author, Eriks Skinkis.



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About Iain Hall

I am married with two children and I live in south-east Queensland.
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9 Responses to Wiper motor wiring

  1. Lloyd says:

    HI there, found this information most useful, used it to wire a two speed Mini wiper into my 1952 Fordson ute, using a standard head light switch. I then took it another step and using a momentary switch and another relay wired on a washer squirter bottle.
    Cheers for the info
    Lloyd

  2. Brian Smith says:

    Oh, handy! Thanks for posting this. I’m trying to run the two-speed with park wipers from a headlight toggle switch on a 1963 Mini, and this is quite helpful.

    After staring at it for a while, isn’t it possible that as the switch is moving from slow to fast there could be a gap large enough (>5 msec) to cause the relay to disengage? Then the fast windings are moving the motor, and the slow windings will be cycling on/earthed.

    I’m not saying it *is* going to happen – much would depend on the switch used – but it *might* happen.

    I think I’ll try running the relay off a pair of diodes, so it’s energized for certain on either fast or slow settings. Belt and suspenders and all that.

    • Lloyd says:

      I am no guru so i just followed the above diagram and it works, the wipers park fine, i used a head light toggle switch for mine, my wipers also park when i use use the push button switch i installed for the washer, i still have a wiring diagram of what i did if you would like it. good luck

      • John Hannah says:

        Hiya Lloyd,can you send me your wiring diagram for the wash wiper as I am rewiring my midget with new switches now,any help is good
        Cheers John

      • Brian Smith says:

        I built it on the bench now (finally got back to working on the electrics) and figured out that my worries were groundless. The spinning motor (at least on a fairly new lightly loaded motor) generates enough voltage to keep the relay engaged for half a second or more even when all power is cut.

        Which leads to a different (though minor) problem I had never thought of: When you switch from slow to off, the motor has to slow down before the relay disengages, then it jerks back into motion as it gets connected to the park switch.

        I think I might go with a 2-relay solution instead, just to avoid that jerkiness.

      • Iain Hall says:

        I only have a single speed motor in my car and it is switched with an A30 switch without a relay for simplicity I have also not wired up the auto park function out of shear laziness but I have become quite good at timing the switch to park the wipers in the right place.

  3. Lloyd says:

    Hi John how do i contact you to give you the wiring diagram????

  4. michael joo says:

    my car,s wiper constantly wiping the windsdreen at fast speed whenever I turn on the switch
    and even though I try to change the speed of the wiper , it does not work ( moving at fast speed).
    could you tell me the possible trouble please.

    • Iain Hall says:

      Sorry Michael but I can’t diagnose your problem from that description it could be brushes or bearings in the motor best contact an auto electrician

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