MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Early wiper switch

I think I need a new windscreen wiper switch on my '66 GT - it's always needed a wiggle before the wipers would park but the other day it needed to be turned on, then off, then on again before the wipers would start - and then it only worked about 50% of the time!

Assuming it's the switch and nothing more suspicious, does anyone know the difference between these three switches available from MG Owners Club spares (I just want to replace the existing Lucas toggle switch):

http://www.mgocspares.co.uk/acatalog/MGOC_Spares_HORN___SWITCHES___WIRING_73.html#l42

42 - Switch - Wiper - Single speed 149011 [42]
Price: £13.35 Including VAT at 17.5%
43 - Switch - Heater fan RTC430 [43]
Price: £4.25 Including VAT at 17.5%
43 - Switch - Auxiliaries BCA4312 Use RTC430 [43]
Price: £4.25 Including VAT at 17.5%

Isn't it just an on-off toggle? Does anyone know why the one specified for the wipers is over 3 times the price of the other ones?! I can't imagine the wiper switch has a higher current rating, is there an additional terminal for parking or something? Or can I use the £4.25 switch for the wipers?

Many thanks,
Tim
T Jenner

It will be interesting to see if I am corrected, but I think the switches are the same for the single speed wiper switch, heater etc.
Ian Buckley

I am with Ian, the switchis just a ingle pole, single throw switch like the one for hte heater fan, but the service parts list show a differentpart number and I know that the switch is a different configuration for the wipers. I think that I would be tempted to try using the fan switch and see if it will work. The only difference that I can think of would be the current rating is higher for the wiper switch, in which case a relay in series withthe switch would handle the excess current.

Your problem may be more than just the switch on the dash. It sounds like your park switch, internal to the wiper motor/gear box assembly may be flakey also. The park switch is supposed to keep a ground to the motor to keep it running when the switch is turned off until the wiers are in the park position. Cheers - Dave
David DuBois

On some models - check the wiring diagram for your particular car - the 'park' circuit goees through the wiper switch, which means there are some NC contacts when the switch is in the 'off' position.
Dave O'Neill 2

Dependes on if your wiper is the early wiper, or the same used in the 67 GT. Which appears to be only in the 67 and perhaps the 66. Single speed motor in the 67 has a unique parking system (three fingers that rub over the back of the gear. Gear has slots in it that break the conductivity. and rerouts the power to park the motor.

The switch can move and actually still not be working. There is a toggle inside that is spring activated, If the spring gets out of place it will not make contact.

Check the conductivity of the switch. If working, check the motor. If it is a round body, it very well could be the same as used in the 67. If so, take the cover off and clean the fingers and the brass plate on the wheel.
BEC Cunha

Thanks for the responses everyone. The wiper motor has a round body (seen from under the dash on the driver's side), but I assumed the park mechanism might have something to do with the switch. The reason I say that is because sometimes if I switch off the wipers they just stop where they are (mid-way across the screen). If I wiggle the switch (not actually switch it, just wiggle the body) the wipers return.

The car is a MK1 but after all this time who knows if it's the right wiper motor for the year! Is there a way to tell by looking at the motor? Would I be OK to try swapping the switch with the one for the heater blower to see if it fixes it or is that likely to overload the switch? Does anyone know the respective current ratings?

Thanks again,
Tim
T Jenner

Tim,
I think the round body motor is correct for a 66 GT - the same as I have in mine. The motor has a clever arrangement of contacts inside it to maintain current to the motor (after they are switched off) to return the wipers to the park position - when they reach this position the contacts are lost. Once you have the motor out of the car it is not too difficult to strip the motor down and check all is well inside. You might want to consider this option before buying a new switch. Go with what BED suggests. Where are you in Surrey?
Richard
Richard Atkinson

Surely if the this wiper switch includes some functionality for parking, it would have more than just the two wires going to it? If so, should be easy to do a visual check. If there are only two wires, I would assume that it is a simple single pole on-off switch.

Also the wiring diagrams should give some additional insight.

Regards,

Barry
BJ Quartermaine

MMMMMMMMM

This is getting interesting because my wipers have not been parking since I last pulled the loom out. However I do not believe there is anything wrong with the wiper motor. Perhaps I do have the incorrect switch there. Mine is a 1964 roadster with the square wiper motor.

I just checked the early wiring diagram and it shows BG and black only. One of each??
Ian Buckley

I'll try to pull the switch over the weekend and take a look - presumably it would have 3 connections if it provided power for parking?

Thanks,
Tim
T Jenner

I just had a quick look at the MGB wiring diagrams available on Gerry Mastermans site http://www.advanceautowire.com/ Diag 2 covering 64/67 MGB has only two wires going to the wiper switch whereas Diag 3 covering 67/68 MGB has five wires on four terminals. It isn;t obvious when the change was made during 1967.

Barry
BJ Quartermaine

Here is a good archive thread that was done when I had problems with the motor in my 67. I have pictures of mine and the different parking system it has.

After a lot of discussion, we determined that this motor and wiring (potentially used for 65 to 67 GT's)is different than most of the wiring diagrams show.

http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=71&subjectar=71&thread=200509160548598636

Paul Hunt is normally a regular on this web page. He has a post on the archive link. He is one of the more knowledgable folks on this topic. He is on your side of the pond also.

You can also convert your system to a two speed. The two speed switch is available and I can send you the wiring to hook up the later two speed motor to it if you want.
BEC Cunha

If it's the earlier switch you need, make a beeline for the nearest wrecker and look for a Morris 1100. I recovered some good Lucas switches this way - $1 a pop is good value!
John
John Minchin

The wiper electrics around 66/67 are a mess, there can be four different motor and switch wiring systems. You can really only go by how many and what colour wires are on the switch.

The earliest and simplest system is single speed, square motor, with black and green/black wires on the switch. This is a simple on/off switch which can be replaced by pretty-well any other type of switch that has at least one on/off pair of contacts. The parking on these is controlled entirely in the motor, which has a black (ground) connection for the park switch as well as green (12v) used for both running and parking.

The latest system was two-speed with a round motor, with green (12v power), red/light-green (slow), blue/light-green (fast) and brown/light-green (park) wires on the switch. This switch has 'normally closed' contacts that connect the park and slow speed wires together when the switch is off, as well 'normally open' contacts to connect the 12v supply to first the slow speed then the fast speed wire. With this system the park and slow wires, the motor park switch, and the manual switch park contact all have to be working correctly for the motor to park.

In between these there seems to have been:

1. An early two-speed system with a square motor, and a simplified switch and wiring with black (ground), black/green (slow) and light-green (fast) wires at the switch.

and 2. A single-speed round motor with the later parking system (colours not available).

Paul Hunt 2

OK, finally got round to pulling the switch - I fear I may have encountered the last of the options Paul mentions - single speed, round motor but later parking system!

I've uploaded a picture of the motor (sorry about the quality, used my phone to take the picture). The switch has 4 contacts and 3 wires connected:

1=Not connected
2=Black/Green
3=Red/Green
4=Black

I THINK red/green (terminal 3) is the live feed; black (4) is earth and black/green (2) is in some way related to the parking mechanism since if I disconnect it the wipers work but don't park.

The switch when removed operates as follows:
OFF - Pins 1, 2 and 3 connected; pin 4 disconnected.
ON - Pins 1, 3 and 4 connected; pin 2 disconnected.

In other words (I guess) pins 1 and 3 are tied together; 1 and 2 are switched (connected when switch is OFF); pins 1 and 4 are switched (connected when switch is ON). It has "34889A T 68" stamped on the side of it.

Does that sound about right for one of the systems or do I have a mixture or bodged wiring job!?

I couldn't find any fault with the switch - resistance is only a few ohms and it seemed to work fine. I cleaned the terminals and it seems to park better now but the non-starting problem is still there. It seems to start if I fiddle with the connections so I guess it's still either a fault with the spade connectors or the switch.

I'll be going to Beauliea at the weekend and will keep an eye out for a switch - is this a "normal" one or could it be a switch from somewhere else??

Many thanks again,
Tim

T Jenner

tim
the switch has been changed as the switch is marked with the year 68 on it
all wiper motors and a lot of the other parts are marked for year which helps if your trying to find the age of a car
the number will always be on or earlier than the year of build
ste
Ste Brown

Post from Barry above

"BJ Quartermaine, Ontario, Canada, bquartermaine@cogeco.ca
I just had a quick look at the MGB wiring diagrams available on Gerry Mastermans site http://www.advanceautowire.com/ Diag 2 covering 64/67 MGB has only two wires going to the wiper switch whereas Diag 3 covering 67/68 MGB has five wires on four terminals. It isn;t obvious when the change was made during 1967.

Barry"

The site you have referred to belongs to Dan Masters and he is the one that drew the diagrams and made them available to all.

Gerry Masterman's site is http://gem-enterprises.net/
Kimberly

Measuring resistance of connections and switches is not recommended as the contacts can develop a film which will show up as several or many ohms, but when you use a switch in a 'real world' situation this film burns off. OTOH when measuring weak connections you may well see very low resistance, but when the connection is carrying a load current it can fail altogether i.e. go fully open-circuit.

The only sure way to check connections and switches is to measure the volt-drop across them when they are carrying their design current, either directly by applying the meter to both terminals, or by measuring both sides with respect to a known good ground. In the case of a switch, when measuring contacts that are closed, you should see the same voltage each side. When the switch isn't supplying a load this voltage will be the same even for very high internal resistances. You have to measure the voltage on-load, and then the higher the current and/or the higher the internal resistance the more difference in voltage you will see.

Tim - that does sound right for a single-speed motor with the later parking system. For a while my 73 had a similar problem in that it didn't always start when switching them on, but as mine are 2-speed and they did always start when switched to the 2nd speed, continuing to run when returned to the 1st speed, I must admit I lived with it for a while and the MOT tester never commented, and for some time now it has been fine (would that the weather had been).

Early switches tended to be 'generic' in that they had several terminals, some make and some break, not all being used depending on the application. When selecting a switch, especially at an autojumble, take a battery and bulb along with you and prove it does have the required make and break functions, and that the brightness of the bulb is the same with the current going through the switch as when connected directly to the bulb. Of course, this doesn't require a 12v battery and bulb, a torch battery and bulb should be fine! :o)
Paul Hunt 2

This thread was discussed between 23/08/2007 and 06/09/2007

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now