Cheers Richard. I'm away until Wednesday so I'll try what you have suggested when I get back. Please excuse my ignorance but can you tell me where the 3 test pins are located and how to identify they as I am still learning my way around this system.

The ECU I'm using is an Autronic SM4. It does have a spare PWM output but I wouldn't know how configure it to the aquamist system.
I am confident with a soldering iron too.