wipers, relay or not?

Hi,

Having trouble making a new circuit for my windscreen wipers.  It's a very old car and I'm adding an intermittent function so I can use one of the positions on the stalk for a timed wipe once very so many seconds...

Anyway, ignore that, it's just background...

The main issue is that since I am having to build a new circuit from scratch I have come across a problem getting the wipers to park after the stalk has been moved to the 'Off' position.  Oddly enough, the wipers will park when using the new intermittent function but if I use either position 2 or position 3 then the wipers will just stop randomly somewhere on the screen.

This is a very basic illustration of what I have.  There are other things like fuses in my real circuit on the car.  The motor has two speeds and that function is handled inside the motor so you just provide current to one wire or the other depending on if you want fast or slow.  The motor also has a park switch which will be connected if the wipers are anywhere other than the parked position.  i.e. the circuit will break when the wipers reach park.  With the basic circuit setup like this I get everything working except that the wipers don't park.

So instead of that, I tried adding a basic relay in like this.

But the problem I have now is that the wipers move too quickly for the relay.  They reach park and then the voltage drops but not fast enough... The relay stays open too long and the wipers come back out of park and perform another wipe... which opens up the relay again!  So they don't stop but you still hear the relay clicking on and off.

I already tried pushing power through that circuit but wires were melting.  I might re-visit that.

I think what I need is a special type of relay which will stay off long enough once the wipers hit park.  At moment, my circuit with a relay works in principle but in practice the current stays too high and the wipers bounce off the bottom an start another wipe.  If I had a relay which just turned off and did not reconnect again straight away then I think that would work!

I've been reading Wikipedia to find out about different types of relays and it looks like a 'latching relay' might do the job.

I would need to connect 1 switch to the 'off' position on the wipers stalk and the other switch to the 'park' position on the motor.  The first connection will be made when the stalk is moved to 'off' - the second connection is made when the wipers hit the park position.  This should mean that the circuit will go dead (obviously depending on the way I wire it up) until the relay sees the wiper stalk going into the 'off' position again?

The park switch is closed while the wipers are anywhere on the screen except park. 

It would make sense to use that as the grounding function for a circuit which would bring the wipers back to the parked position as it would be on whenever the wipers were away from park.

I think I see where you're comming from with regards powering the park switch.  But the original functionality in the connector block of the wiper motor has been disabled as I cut the wires which come out of the connector and feed to the motor.  I did this so I would be able to power the motor directly and have proper control of the motor without any extra inteligence in the connector messing things up.  Like in the diagram above, there are three wires comming out of the motor.  The park switch is on the connector block and that still works. 

IIRC there are 5 other poles on the connector block which I'm no longer using.  I tested these poles under various conditions and found nothing else of any use apart from the park switch.  One of the poles was looped into the other so I know both of those would have got power originally. 

What made me chop the link between the motor and the connector block was that I am using two different types of circuits from two different cars.  The original circuit had no intermittient function and it used a different wiper stalk.  So the new circuit is quite different from the old one.  The new circuit only requires some basic functions from the motor. One of the things the new motor can do which the old one can't is to self-park without any additional wiring.  The new motor has 5 poles so that the intermittient wiper relay can be connected to the park switch.  My new circuit parks ok when using the intermittient function as it is wired up the same way as the new circuit would be.  It just won't park by itself without me doing something extra... yet to be identified.

Diodes will not work. 

Cold side of the park switch connects to the ground motor terminal and the wire from the new relay.