Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Intermittent Wiper Control

Hi,

I have a 1995 4/4 which has no intermittent wiper control on it. I decided to fit the Smartscreen device which allows intermittent control between 5 and 30 seconds. Although a pain to get into the Morgan wiring the device works well.

However I am concerned that to operate the device you have to flick the wiper lever twice to set the intermittent period. I am concerned that this will cause a lot of wear on the wiper lever. I decided to fit a spring loaded toggle switch across the wiper lever to give a momentary contact. Unfortunately this blew the wiper fuse. I concluded that the wiper switch must put a short to earth on the supply from the switch contact to the wiper motor when switched off. I have come across such arrangements previously to help slow motors but I am not clear why this would be done in this application. I have been advised that the wiper switch was originally from a Triumph Herald but I am not sure if that is true.

I have thought about a work around by using a diode but before I try that I would like to understand why the short is used in the first place.

So anyone have any clues please.

Cheers

David

David, I have not got a clue as to what set-up might be for your wipers wiring but from a very dull memory, the park position was adjustable at one time by rotating the round tin top cap on the wiper motor once the screws were loosened off.

As best I can remember inside the top of the cap was insulated with a very thin sheet of plastic with a cut out in it a bit like a pie chart with circa 15% cut out and exposing the metal of the cap. There was a an electrical wiper arm mounted on the gear motor gear wheel that made contact with the top of the cap internally running round it`s circumference continually while the wipers were switched on. The idea being that the electrical wiper continued to provided an earth to the motor when the earth supplied by the wiper switch was switched OFF, thus the motor would continue to run till the electrical wiper hit the insulated section on the inside of the cap, at which stage the earth was lost and the motor stopped.

Adjusting the park position was achieved by loosening the screws around the wiper motor and rotating the cap. Some of this type of wiper motor had an earth wire connecting on to the centre of the cap externally.

Hope I have not served to muddy the water..?

Luddite,

Many thanks for the information. I did know about the wiper motor arrangement but forgot about it many years ago, so your comments are very pertinent. I have been assuming the problem lay with the wiper on/off switch but I think a bit of investigation into what happens in the motor when switched is warranted. I have a lot of experience with industrial wiring and what happens in cars is often a surprise to me. So I thought the motor was unlikely to be the culprit but it is now worth investigating.

In industrial motor controllers it is not unusual to have the motor terminals shorted (often via a low value resistance) when switched off and this uses the generator mode of the motor to stop it quickly. However I do not see the need in this application.

I will post an explanation as and when i find it (he said with hope).

Thanks again,


David

It may not be relevant, but as there is a fair bit of overlap between Land Rovers and Morgans. Would this fairly common and straightforward upgrade used on Defenders be an easier solution?

Brian,

Many thanks. I wish I had seen that before installing the unit I have.

Cheers


David

Hi,

Just an update. I found this description and circuit diagram of a two speed wiper circuit which proved invaluable: http://www.netlink.net/mp/volks/schem/wiper.htm.

The short is actually in the motor itself and is there to slow the motor quickly into the parking position. This helps it hit the same parking spot each time. I now need to make sure the Park link to earth is opened before by switch applies power to the motor. So I will try a two pole make before break changeover switch .

Thanks again for the comments.

David

I had a look around and found this:

https://www.franzose.de/de/Citroen-2CV/Alle/Scheibenwaschanlage/ANR14198/

In cause HELLA builds a great kit for classic cars I think it would the old MOG. It looks like a full kit which must „only wired in“.

René