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MG Midget and Sprite Technical - Wiper motor check - non Spridget

Electrical advice needed please!
2005 Astra hatchback. Non working rear wiper so I bought a second hand replacement. Unable to check it on the car as that is 180miles away (arms not long enough) so wanted to check it with a good 12v battery in the workshop. The feed cable has a black, a brown and a blue wire.
The mounting is plastic and it is fitted to the car via rubber bushes so I believe it doesn't earth via its mounting to the chassis. Assume then that black is earth and the other two are power feed and self park feed. Connecting black to the battery negative, with a bulb in series, the bulb lights with the brown connected, but not when the blue is connected.
The motor does nothing! I suspect it is seized and may dismantle from the wiper shaft (gears!) and try again. But is there something else about this that I need to understand?
GuyW

Guy

I think a lot of moderns use brown as earth.

You might want to check it with an ohm-meter
Dave O'Neill 2

With a 12v bulb in series, you may have too much volt drop across the bulb. Can you not rig up a series fuse instead?
Bill Bretherton

Or you could post your question on the BB for Opel / Vauxhaul owners where they probably have pertinent, exact data on how to solve your problem. I'm not trying to be mean, I am just at a loss as to why this is on a Spridget BB. I just did a search for "2005 Astra rear wiper wiring diagram" and found a plethora of information. Not posting it here since it's non-spridget and I don't know your vehicle specifics - just saying....
Stan Kowznofski

Stan

For Spridget owners, this is often the first - and only - stop for technical questions, Spridget or otherwise. We aren't picky.
Dave O'Neill 2

Guy,

Stupid questions, did you check the fuses? Did you have a look on Youtube?

Flip
Flip Brühl

Stan,
I post the question here because this is where my friends are. I have been on this BBS community since around 2007 and it has always been my first port of call. But thanks for that suggestion, I will explore further on the Opal/Vauxhall boards . But at this stage it seems to me that it is pretty irrelevant what the car model is, its just an electric motor that needs testing.

Flip, yes fuses on the car were the first thing I checked. I then disconnected the 3-wire plug from the motor and got 12v readings between the black and each of the other two, from which I deduced there was power to the motor, but that one had failed. That's why I bought a replacement, though now I am not sure that this one works either. Hence my attempts to test it on the bench.

Dave, what or rather how would I check with an ohm-meter? Continuity? Or windings resistance perhaps, but what readings might I expect?

Bill, Once I got the bulb to light, confirming a circuit, I then tried the same connection without the bulb in series but still no movement from the motor.
GuyW

Guy

This is part of a wiring diagram for a Vauxhall Omega, showing the rear wiper motor 'M8' (in a red box).

The earth rail is the (almost) vertical line on the left hand side. You can see that most of the wires connecting to it are labelled 'BR' for brown/braun. I've put a brown circle around a few of them.

The two wires coming into the motor from the right are labelled 'BL' for blue/blau and 'SWVI' for black/Schwarz & violet. The blue is from the relay and the black feeds the park switch.

The image will probably be a bit small, so I will email you the full-size image.

If you earth the brown wire and connect 12v to blue, it should work...hopefully.


Dave O'Neill 2

The title noted it was not 'Spridget' and this side of the pond, on this board we are very willing to help each other - no keyboard warriors here !

'just saying....'

R.
richard b

Guy
In general, most rear wiper motors have an earth, a switched power feed and a permanent feed
So going by that diaghram, In your case I believe the Brown is earth the Blue is power in from the switch/ relay and Black is permanent power (Acc or ign fed)

So earth on the brown and power to both black and blue and it should go then disconnect the blue while it's going and it should continue to run till it gets to the park position where the contacts in the wiper gear assy will disconnect the circuit from the black and the motor will stop--in the park position

It should run with power to blue and earth to brown but might not unless the black is powered up as well just depends on 'what's in the box' some wiper motors need both powers to operate depending on the layout of resistors/diodes, switching etc in the motor/gearbox itself
William Revit

Thanks again. Inspired enough to try out your advice I have just been to the garage to give it a try. (It's 3.15am)
Sure enough, it does exactly as Dave and Willy describe. Brown is earth, not black as I had assumed. Blue and black both connected and it runs. Disconnect blue and it continues to the park position before stopping. Perfect!

The point was the original on the car has packed up. I did check the feed plug had power though working with limited access and poor light I had thought I had the black as earth, but cannot have done. I did get 12v power readings though.

The car is my son in law's, and is up in Scotland. I bought a 2nd hand replacement (£14 as against around £150 for a new one) but had it delivered to my home address so I could check it first (√) and will take it with me to fit next time I visit, probably In a month or so.I

Thanks again, and seasonal best wishes to all!

GuyW

This thread was discussed between 15/12/2019 and 16/12/2019

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