LUCAS 2 Speed Windscreen Wiper Wiring

The Lucas windscreen wiper motors fitted to many Triumph cars have a single speed. Many people have looked to improve things by fitting a 2 speed version of the motor. I have featured the following article by Erikis Skinkis for sometime now. Recently Geoff Morgan contacted me to suggest an improvement. Click here to read about it.

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The Dark Secrets of Lucas 2 Speed Windscreen Wiper Wiring - by Eriks Skinkis

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 swithch/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 not work, but does as you will see in my explain a little later.

Click on diagram to see a larger version

(click on image to see a bigger version)

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:

pin connections on the Wiper Motor

1 - Earth

2 - Auto Park switch

3 - Fast

4 - Auto 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 could then setup the switch  to have: Off - Intermittent - Slow - Fast.
 
The above article may be reproduced for non-commercial purposes only, and full credit given to the author, Eriks Skinkis.
 
[Go to Home Page of Briks Skinkis]


Two-Speed Lucas Wiper Motor Wiring

I am not an automotive electrician, but I have wired my own kit car completely, which includes connecting up a Lucas 2 speed wiper motor without the luxury of the original loom and switch. Some information was obtained from the net, some by bench testing for confirmation.

The diagram below shows how to wire up the 2 speed wiper motor using two single pole double throw (5 pin) automotive relays. The isolating switch used below is a simple 2 pole switch in which both output pins are live in the fast position. Relays do not have to be used, but if using a switch it is important to use the correct Lucas wiper switch (part No #35927). The Lucas motor stops in the park position very suddenly by shorting the windings to ground and if the correct switch is not used, you will blow fuses or worse.

If you are not 100% certain of the identity of the wires in the connector plug (there are various colour combinations) I strongly recommend you do a bench test.
Geoff Morgan

Geoff Morgan circuit diagram

v2

How is a factory 2 speed wiper motor wired

2 speed motors use a switched resistor. When the resistor is switched into the circuit the motor spins faster.