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MG MGB Technical - Lucas 14W wiper motor problem

Hi everyone,
I fitted an MGB 2-speed wiper motor to my MGA a few years ago and it has worked really well.

However, a month or two ago on a particularly wet MGA weekend tour, the wipers began to play-up.
They switched on ok and operated on both slow and fast speeds but they seemed really reluctant to switch off.

Sometimes they would continue running for a few minutes after I switched them off.

I put this down to the sheer amount of rain we experienced over that weekend which may have been shorting out the wiring on the motor and I hoped the problem would disappear once the car dried out.

The car has been in the garage now for a couple of months and I thought I would check out the wipers.
Well the problem is still there and is now even worse.
The wipers just will not not switch off unless I turn off the ignition.

So before I tackle removing the motor (not easy on an MGA) and taking it apart to look at the parking circuit, has anyone any other suggestions about what I should be looking at?

Cheers
Colyn
Colyn Firth

Unlikely to be water, it would have to be dripping off the motor or dash switch, and I doubt water would be able to carry the normal level of current for any length of time.

It could be the park switch sticking. This has a change-over contact operated by a peg that runs on a cam on the large gear wheel. I think the peg drops into a recess at the park position, so if it sticks it won't do that but keeps power to the slow speed winding instead.

However if the peg is lifted by the cam at the park position (must find that out) it won't be that, but the peg could be worn or the switch not operating correctly.

The park switch is part of the five-pin connector, and there are two types - one screwed to the case and one with a spring-clip - more info here http://www.mgb-stuff.org.uk/ws.htm#2sp. Both have been available in the past although the screwed type is rarer.

OTOH it could be the earth at the connector is not going through the park switch for some other reason. This type of motor changes 12v to run the motor while parking to an earth when it reaches the park position, which stops the motor pretty-well instantly in a reliable and consistent position. If that earth isn't connected the motor only slows down over a period, and it might go so far as to operate the switch again and reconnect 12v to continue running the motor. If that is happening there might be an audible slowing down and speeding up of the motor. This might not be noticeable at the blades because as they change direction they slow down then speed up anyway.

All these effects could be random according to voltage, how fast the blades move across the screen, temperature, and so-on.
paulh4

Thanks Paul
I was just in the process of unbolting the wiper motor when I thought it would be sensible to put the question to the forum first.

I will now remove the motor and wire it up off the car to see if the fault is due to a poor connection.
If the wiring is ok I will then take the crank-wheel cover off to see whats happening to the park switch.

Thanks again for your input

Cheers
Colyn
Colyn Firth

The switch is on the back of the large gear so you can't see what it is doing.

To test the switch you can remove it from the case and operate the peg by hand, and if it stops the switch smartly the functioning of the switch should be OK.

With the clip-on type at least you can also remove the cover, and with it clipped back on you should be able to see the peg going up and down and operating the contacts as the motor goes round, although I haven't tried that myself.

paulh4

That's a really helpful picture Paul, I didn't realise that the park switch was actually a part of the 5-pin connector block.

I have taken the motor out of the car to have a closer look at it today.

I do have a spare MGB wiper switch and a spare Lucas 14W wiper motor and I used these to make up a temporary wiring loom so that I could test the two motors.

The spare motor worked fine, it had no crank-wheel in it but when I pressed the park button, the motor parked ok.

However, when I then connected this temporary loom to the cars motor, it ran instantly and would not stop, even when switched off.

I haven't had time to remove the crank-wheel yet to look at the park switch but it's looking like that is where the problem lies.

I will have a look at it tomorrow and let you know what I find out.

Cheers
Colyn
Colyn Firth

The motor gets two sources of 12v one through the switch and one which by-passes the main switch and keeps the motor live until the parking switch ends that input.
Allan Reeling

They both must be there, as it's both running and parking. The problem is that the 12v supply at the motor that's used for parking is not being disconnected and replaced by an earth, which is what the park switch is supposed to do when the cam reaches the park position.
paulh4

Well I am getting closer to finding the problem but not quite there yet.

I have connected the spare motor to the cars wiring loom and it doesn't run at all? although it ran fine when I connected it to the temporary wiring loom out of the car.

When I first fitted the motor to the MGA I used a 6-pin plug and socket to make it easier to remove it from the car for servicing.

I would bet that the problem lies somewhere in amongst those 12 connections on the plug and socket, or the 5 spade connectors on the motor!

I'm beginning to think that rather than try and find and fix the bad connection, it would probably be best to start afresh and make up a complete new loom for the motor with all new connectors.

Ah well!, I was looking for a project to do on the car over the winter :-)

Colyn
Colyn Firth

If the two motors are the same and the one works - albeit not parking - then the other should as well if they both work hooked up outside the car. That might seem obvious but testing wire for wire should reveal the problem.

To run at either speed all that is needed is 12v and earth on the park switch/connector spades shown in my second post.

If the motor is only plugged in and not bolted up to the rack and the body it could be that the earth is not getting through via the connector, in which case the body of the motor will be at 12v.

The spades in the attached connect to the motor brushes, with the wiring on the spades test for 12v on the two side-by-side (fast on the right and slow on the left) and earth on the one at right-angles. If you don't see 12v then test each one against a known working 12v and earth supply to see which one is missing ... could be both!



paulh4

Paul,
you just made me realise something, when I plugged the motor back into the loom to test run it on the car I hadn't connected the earth wire that is normally bolted to the mounting plate. Also, I had the motor on its mounting plate resting on an old towel so it didn't scratch anything!

So there was no earth connection!

I will give it another try "avec prise de terre" (with earth connector) and let you know how it turns out.

You may just have saved me quite a few hours of re-wiring.

Fingers are crossed.

Thanks for the input Paul

Colyn
Colyn Firth

My pleasure, it's not called 'electrickery' for nothing :o)
paulh4

Yup! you were spot-on Paul although at first, when I re-connected the overlooked earth strap, the motor still didn't run.

Then I realised that the earth strap grounded through the new motors base-plate which wasn't bolted to the chassis.
So as soon as I rigged up a temporary earth supply, the motor ran perfectly on both speeds and parked too.

So a great result Paul and very impressive, you were one step ahead of me all the way :^)

Fitting the wiper motor on an MGA is an awkward job on an MGA, its tucked away under the bodywork and it is a struggle to see or to get your hands onto the set screws. You really need one of those body slings that they used in the Mission Impossible film to lower you down to the job from above the car:-)

Also I used to wonder why so many MGAs have been re-painted red, that is until I tackled a job like this one. Its so that the bloodstains from your ripped knuckles blend in with the paint. :^)

Finally, you may have wondered why I was a little reluctant to start again and replace the wiring on the motor.
Its because I made up a special loom with two relays which allow me to use the MGAs pull switches instead of the special MGB toggle switch.

I will try to upload a picture or two to show this.

The first picture shows the new motor on its new mounting plate. There are 2 micro relays (black) mounted on the new mounting plate. At the front of the picture is the loom I made up to connect to the car through the white multi connector plug seen at the lower right of the picture.

Cheers
Colyn


Colyn Firth

This is a picture of the MGB motor installed in my MGA.
You can see the white connector at the top left of the picture, one of the black mini relays on the right and the earth strap (which I forgot about) on the left where it is bolted onto the mounting plate.

Cheers
Colyn

Colyn Firth

Kudos for a neat installation, and sussing out what needed to be done to replicate the 'changeover' function of the of the later MGB switches so you could keep your originals.

paulh4

Paul. my 2-speed conversion went so well that I wrote up the whole process for the MGCCs MGA Register for anyone to copy.

I got the initial idea from Dominic Clancy in Switzerland and also from Barney Gaylords MGA Guru website in the USA.

Barney designed the twin-relay circuit and has done a great schematic circuit diagram on his site.

This is the link to my write-up.

https://www.mgcc.co.uk/mga-register/wp-content/uploads/sites/22/2013/12/Safety-Fast-2-speed-wiper-article-updated-version-dec-13.pdf

Cheers
Colyn
Colyn Firth

Fair-do's for giving credit where it is due, but you still implemented the working system and wrote it up very well :o)

I'll put a link to your document on my site as electrically and switch-gear at least the situation for early MGBs is the same.
paulh4

Cheers Paul,
can you let me have your websites name so that I can have a look at it.

Since fitting a 1950cc 5-bearing MGB engine to my car I have begun to look much more at the MGB websites and Forums and I have found some really useful information on them.

Thanks
Colyn
Colyn Firth

Sure - http://www.mgb-stuff.org.uk/hometext.htm, and click 'Spanners' on the left for all the techy stuff.

paulh4

Colyn,
Paul's site is excellent, very comprehensive and a lot of the information can apply to other MG models and other marques, prepare to lose a good few hours (each visit).

The link Paul put up accidentally included a comma so try below and click 'Spanners' (l/h top menu) -

http://www.mgb-stuff.org.uk/hometext.htm
Nigel Atkins

Thanks Nigel,
your revised link did the trick, you are correct, it is a great website.

You may not hear from me for quite a while now :^)

Cheers
Colyn
Colyn Firth

Sorry about that.
paulh4

Paul I only noticed the comma when I went to copy&paste to wotsit bar.
Nigel Atkins

Yes that's when it causes the problem :o) The other thing is that sometimes when pasting to the forum http becomes https and that also causes a problem.
paulh4

This thread was discussed between 08/01/2019 and 16/01/2019

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