The windscreen wipers on my Aero 8 lifted off the screen at 70mph so I slightly increased the pressure by bending the wiper arms a tiny bit as I did on my old +8 in the past. Unfortunately this has now resulted in the wipers refusing to stop once switched on even when the ignition key is removed.
If you hinge any of the three wiper arms off the screen the others work perfectly. I have reduced the pressure on the nearside and middle blades and all appears well but once again they are useless at clearing rain off the screen. Does anyone know why this should have happened or have any ideas of how to improve the performance of the wipers?

What a strange fault; certainly a new one for me on the Aero 8

Like you, I have bent the arms to increase downward pressure; however, I did not experience an issue with the wipers then staying on.

I was once able to buy an accessory airfoil that fitted on top of the wiper arm and exerted down pressure at speed. Was years ago so I don't know if they are still available.

..all I can think is the bending has caused the park switch to loose contact, which when released (or hinged) causes contact to be remade.

That said I cannot picture how....

If the key is removed from the ignition switch, the wiper circuit should be dead. It might be worth checking the circuit diagram to see if that is the case.

I suspect that this is something to do with the arc of wipe. Wipers switch off when the park position is reached. In theory if the added pressure prevents the park position being reached, they will do another wipe.
Just a theory.
But not switching off with the ignition implies a relay fault which can't be directly related to bending the arms..........

..but wouldn't this lead to parking the wipers in a different position?

Doesn't make sense does it!!!!
If the wiper motor is conventional it shouldn't be possible to continue running, or miss the park spot, especially with the ignition off. I would start with the relay.

Certainly food for thought. Thank you for all your comments. The suggestion that they didn’t reach the park position seems feasible if it wasn’t for the fact they stay on when the ignition is off. At our Noggin tonight so do doubt the wipers will get plenty of use in our British summer. Thanks you all, I will keep you posted when I get it resolved.

On a couple of cars I've had in the past, there was a re-set routine for the park position of the wipers. A re-learn, if that makes sense. Perhaps the factory or a dealer might know what that is.

I suspect, as already posted, the park position has been lost.

I assume with the Morgan that the wipers return to 'park' when the ignition is turned off - ie they don't stop suddenly in a vertical (or wherever) position?