90 wiper switch wiring

[chaincommander]

Hi all,

My 90 wiper switch has a position for a single sweep, but it doesn't work. The low and high speed positions work fine, but with the intermittent rain we've been having the last few days, I was thinking I would like to be able to get just one sweep now and again. So, knowing (or thinking I'm knowing) a bit about electrics(house electrics, TV's but not vehicle), I dismantled the switch to see if I could spot the problem.

I ended up confused and no further forward. The switch body has 4 brass pillars, each of which has a wire coming out of the back. The switch lever moves a spring loaded brass cylinder up and down over the 4. So in the low speed position, the spring loaded brass connects 2 and three; in the high speed position, pillars 3 and 4 are connected together.

It's kinfd of cunning, the spring loaded brass falling in between the fixed brass pillars gives the switch it's 'click stops'.

Now to the bit that confuses me. In the off position, the switch seems to be connecting pillar 2 to pillar 1, and in the single sweep position, it doesn't connect anything together, the spring loaded brass just rides up on pillar one.

The wiring diagram I have is not much use, it shows a blank circle containing all the console switches, and the wiper motor has 4 wires going into it, but no explanation.

Has anyone managed to figure out how this all works?

It

[SimonHobson]

My 90 wiper switch has a position for a single sweep, but it doesn't work.

I think early ones were like that !

I ended up confused and no further forward. The switch body has 4 brass pillars, each of which has a wire coming out of the back. The switch lever moves a spring loaded brass cylinder up and down over the 4. So in the low speed position, the spring loaded brass connects 2 and three; in the high speed position, pillars 3 and 4 are connected together.
...
Now to the bit that confuses me. In the off position, the switch seems to be connecting pillar 2 to pillar 1, and in the single sweep position, it doesn't connect anything together, the spring loaded brass just rides up on pillar one.

OK, ignition supply comes to pin 3, 2 & 4 go to the motor (slow and fast respectively). Pin one comes from the park switch and is live when the wipers are not parked, and earthed when they are.

When you switch the wipers off, the slow speed connection is fed by the park switch. When it parks, the slow speed connection is earthed, shorting out the motor, and electrically braking it to a quick stop.

[chaincommander]

Simon, thanks, that helps a lot but I still don't quite get how the single sweep works.

Sorry to be a pain, and this has been a great help (I was thinking I could wire a push button from 12v to the low speed wire to make it go, but clearly that is not a sensible idea when the low speed wire is grounded, so you have saved me a blown fuse and a fright.)

Moving the switch to the single sweep position simply removes the ground from the low speed wire. What makes the motor start to move?

bob

[SimonHobson]

Simon, thanks, that helps a lot but I still don't quite get how the single sweep works.

Sorry to be a pain, and this has been a great help (I was thinking I could wire a push button from 12v to the low speed wire to make it go, but clearly that is not a sensible idea when the low speed wire is grounded, so you have saved me a blown fuse and a fright.)

Moving the switch to the single sweep position simply removes the ground from the low speed wire. What makes the motor start to move

Simple - it doesn't ! Early models didn't have this function although the switch appears to have the position for it.

Possibly the easiest way would be to fit a later switch. Failing that, could you can add an extra contact so that when the roller rides up on terminal 1 alone, it can touch a small wire or something. You can then connect a relay coil between this wire and terminal 3. As the roller must be clear of terminal 2 when this relay is energised, it can simply connect terminals 2&3.

When you push the stalk down, the roller will contact the wire, the relay will pull in (because terminal 1 is earthed by the park switch), and the wipers will unpark then stop as the relay loses it's earth. When you release the stalk, it will link terminals 1&2 and the wipers will complete their cycle before parking.

I think you'll find a later switch easier and more intuitive in operation.

[chaincommander]

Simple - it doesn't ! Early models didn't have this function although the switch appears to have the position for it.

Possibly the easiest way would be to fit a later switch. Failing that, could you can add an extra contact so that when the roller rides up on terminal 1 alone, it can touch a small wire or something. You can then connect a relay coil between this wire and terminal 3. As the roller must be clear of terminal 2 when this relay is energised, it can simply connect terminals 2&3.

When you push the stalk down, the roller will contact the wire, the relay will pull in (because terminal 1 is earthed by the park switch), and the wipers will unpark then stop as the relay loses it's earth. When you release the stalk, it will link terminals 1&2 and the wipers will complete their cycle before parking.

I think you'll find a later switch easier and more intuitive in operation.

Man, you have no idea how much time I wrestled with this today, trying to figure out if a pull up resistor could be there somewhere that would allow the motor to start just enugh to unpark .

But a later switch sounds easier. Many thanks for the help, all clear now.

bob