410 Wiper Motor Wiring

[DODD]

Roger,

Follow on from my last reply on another thread; I would like to carry out a modification to the windscreen wiper motor on my 410. I would like to wire in a momentary toggle switch into the circuit.

As you know the wiper controls on a 410 are:- off, on normal and on fast. If you want an intermediate wipe it’s a case of a quick turn of the switch and off again.

When the insulation to the wiring on the wiper motor started to breakdown through old age last year, it was necessary to rewiring the wiper motor box. I thought at the time it may be possible to wire into the existing circuit a momentary toggle switch. Judging by some of your other replies in the forum you may have the answer as to whether it’s possible and also knowledge of a wiring diagram?

I would appreciate your thoughts or anyone else who may have done this modification.

Brian

[Thomas591]

Hi Brian,

I have attached the wiring diagram which should be ok for your car.

The solution is not that difficult:

One contact off the momentary toggle switch should be connected to terminal 5 on the washer switch, the other contact to ground.

This should operate the wiper motor when the main wiper switch is in the off position as long as the toggle switch is pressed.

Hope that helps (and will not set your car on fire :-) )

Thomas

[DODD]

Thanks Thomas,

It sounds too easy.

What rating do you think I need on the toggle switch and should I feed it through a relay?

Brian

[Thomas591]

Brian,

I think nothing is needed here. any standard automotive switch should have more than enough amperage to handle the wiper motor. But make sure you use Off- Spring On toggle switch not a standard off-on switch for functions requiring a momentary on switch like windscreen washer etc.

Thomas

[Roger Morrall]

Goodness me! Congratulations Thomas591

I’ll admit I had spent quite a lot of time thinking about the possibilities, but I never came up with anything useful. Somewhere I have all the switching logic worked out and I’ll be looking it out on the next rainy day in order to satisfy my intellectual curiosity as to how this works (not that I’m doubting that it does).

I was aware that the wipe - park switching relied on a clever wiper motor reversal and a degree of slop in the motor to achieve the park position, also that Rolls Royce got Lucas to produce a RR version that somehow avoids the annoying smear in the centre of the screen when the wipers go to the park position, but I’d have given my (rather rotten) back teeth for this one.

From memory the motor normally takes about 5 amps and it’s stall current is something like 15 or so amps, in either case any modern automotive switch will cope. But always avoid stalling the motor (which is very possible with modern wiper blades and a dry screen) as the motor will eventually burn out - the power to the motor is only cut off once the wipers are actually parked.

Roger

[DODD]

Hi Thomas,

Thanks for your advice yesterday.

Just finished the wiring and now waiting delivery of the momentary toggle switch, which should’ve arrived this morning. I have tested the circuit and it works perfectly and the wipers park where they should.

For simplicity, I connected into the existing circuit adjacent to the wiper motor and fed the wire through to the dashboard. Literally a ten minute job.

I think it will take a bit longer to actually install the switch though.

I am sure a few other Bristol owners will also do this modification.

Brian

[Thomas591]

Hi Brian,

good to hear that it really works...
I invested some late night hours to understand the wiper mechanism as I want to install a optical rain sensor behind the rear view mirror which will operate on stage one of the wiper switch. This should enable the wiper to regulate the interval of the wiping by itself. I have already all necessary hardware (sensor and control unit) but haven't tried it out yet.

Regrads

Thomas

[Roger Morrall]

Originally Posted by Thomas591

Hi Brian,

I have attached the wiring diagram which should be ok for your car.

The solution is not that difficult:

One contact off the momentary toggle switch should be connected to terminal 5 on the washer switch, the other contact to ground.

This should operate the wiper motor when the main wiper switch is in the off position as long as the toggle switch is pressed.

Hope that helps (and will not set your car on fire :-) )

Thomas

Take great care - looking at the circuit diagram you posted - which is specific to the 411s - I note that IF the regenerative braking has been activated by the limit switch (This is only a possibility, NOT a certainty) Terminal 5 will be live. The 410s used a slightly different system which I’m fairly familiar with but which I haven’t yet investigated in this respect. I may be in a position to look at the latter and post some illustrative circuit diagrams shortly, in the unlikely event of course that it continues to rain here in West Wales.

I’m understanding both Thomas and Brian imply that a momentary earth on terminal five achieves a full wipe through the normal wiper arc. I’m struggling to get my head round this, given that the motor is running in reverse which is normally used to achieve the park position which is outside the normal wiper arc, can you please both confirm? (I think you’ll be getting a 2/3rd wipe)

I bet nobody knew that 411s (and others) employed regenerative braking long before the EV boom, albeit only in the wiper motor!

[DODD]

Hi Roger,

You are correct that the connection to terminal 5 will only give a 2/3rd wipe but the arch of the wipers is sufficient to completely clear the driver’s view but not all of the passenger’s side of the windscreen.

To operate the wipers via the toggle switch, you have to give the switch a reasonably quick press. The reason for this is if the press is too quick the wipers will move slightly further into park position and not travel across the screen.

Irrespective of whether the wipers have been operated via the main switch or the toggle switch in any sequence, operating the toggle switch will always move the wipers further to the park position, albeit only by a fraction before moving across the screen.

When I initially checked if Thomas’s proposal would work on my 410, I used a test wire with a 5amp inline fuse just in case the 410 was different to the 411. I decided to keep the 5amp inline fuse in the final wiring as a safety measure.

All in all, I am very pleased with the performance of the addition and I still have the option of using the main on/off switch for a single wipe if required but if you can see an alternative sequence for wiring the momentary switch into the circuit, I will be happy to try it out, as it’s a very simple procedure to swap the wires around near the motor.

Brian

[DODD]

Roger,

I should have mentioned in my previous posting that since I have owned my 410, when turning on the wipers, I always get a 2/3rds wipe, before a full sweep of the windscreen.

So, when I want an intermittent wipe using the on/off switch, I have to pause over the switch until the 2/3rd wipe has completed its cycle; this is then followed by a full sweep of the wipers. Because of the delay I usually accept a 2/3rd sweep, which I find is sufficient.

I don’t know if this is a common problem to other 410’s or one peculiar to my car; it’s possible that prior to my ownership, someone has transposed one of the wires, whilst working on the car.

Brian

[Roger Morrall]

I’ve been thinking about this and am well on my way to writing a thesis on the Lucas 6 Watt and 16 Watt wiper motors that were used on the 410s and 411s respectively.

Brian - Your 410 wiper motor is behaving exactly as I’d expect it to, I don’t think any previous owner has changed anything. You are bypassing the limit switch when you ground terminal 5. The limit switch goes to ground anyway and opens in order to stop the motor when the wipers have reached the park position. So bypassing it means that you are causing the motor to run on slightly beyond the park position before it then then starts the next sweep. You have to keep your finger on the switch that you are using to ground terminal 5 for long enough allow the limit switch to close again to allow the sweep to continue. You are quite safe in grounding terminal 5 because that is only ever connected to earth via the limit switch. THIS IS NOT TRUE OF THE 411 WHERE TERMINAL 5 CAN BE LIVE IN A NUMBER OF CIRCUMSTANCES- the 411 motor and it’s wiring and it’s switching logic is entirely different to the 410s

The change between the wiper operating arc and the wiper parking arc is achieved by 1) a degree of play engineered into the crank arm that drives the rack that runs to the wiper wheel boxes 2) reversing the motor so that then drives the wipers in a different arc. Each motor reversal between slow-to-stop and stop-to-slow has to take up this play which is why you get the 2/3rds wipe before the wipers then take up the full wipe pattern and also the 2/3rds wipe before they shut down

You could perhaps build a timer and a relay into your circuit to give a timed operation of the wiper off a single tap on your momentary toggle switch

[DODD]

Roger,

Many thanks for your detailed explanation.

I like the idea of the timer, if I install the timer I will still only get a 2/3rds wipe on each movement across the windscreen using terminal 5 but I intend to install one anyway. I will replace my existing single pole momentary switch with a double pole. This will allow me to have a single 2/3rds wipe on one action of the switch or say 3No. 2/3rds wipes on the other action, according to how long the timer is set.

I have sourced the switch and a time delay relay which should be with me tomorrow.

Brian

[Roger Morrall]

Good thinking - I think most time delay relays give you a live output as opposed to an isolated contact so you’ll perhaps need to take that output to a relay to switch your earth. Does that make sense?

[Roger Morrall]

Originally Posted by DODD

Roger,

Follow on from my last reply on another thread; I would like to carry out a modification to the windscreen wiper motor on my 410. I would like to wire in a momentary toggle switch into the circuit.

As you know the wiper controls on a 410 are:- off, on normal and on fast. If you want an intermediate wipe it’s a case of a quick turn of the switch and off again.

When the insulation to the wiring on the wiper motor started to breakdown through old age last year, it was necessary to rewiring the wiper motor box. I thought at the time it may be possible to wire into the existing circuit a momentary toggle switch. Judging by some of your other replies in the forum you may have the answer as to whether it’s possible and also knowledge of a wiring diagram?

I would appreciate your thoughts or anyone else who may have done this modification.

Brian

I believe that I have come up with a good solution* to Brian’s original query, as posted above, which I’ll publish when Brian has had the opportunity to check it out.

* ie one, two or three full wipes and back to park from a momentary toggle switch

Whilst addressing how this might operate on a 410 I’ve also looked at the 411 (which uses a different wiper motor and switching logic) and I think I have a similar solution for the 411s. If anybody from the 411 fraternity is interested in pursuing it please send me a private message and I’ll email a copy of my suggestions. Anybody that is who is capable of following a simple wiring diagram involving a couple of changeover relays and a timing relay AND is prepared to commit to give me and hence the rest of us the appropriate feedback.