Hi Martin,
If you unplug the main control harness from the motor does it still beep when the power is turned on?
If the beep disappears, try this simple test to see if the controller and motor are working correctly:
Make sure the wheel is raised off the ground and that the power is switched
ON before you insert the wire.
Be very careful to only put it into the correct holes or you could damage the controller or wiring.
Don't force the wire into the socket or it may open the contact too much, simply touching it against the two contacts should be sufficient to make the motor run if the controller and motor are OK.
I also am very puzzled by the constant beep as I don't recall hearing of this particular fault before, usually there is a series of beeps which are used to give an indication as to what is causing the fault.
If all of your non-working Qugos are emitting a constant beep I suspect it may be something to do with the wiring that is specific to the Qugo.
In your original post, you mentioned that the "brakelight works perfectly", but brake lights are not catered for on the Magic Pie's wiring harness, so how exactly has the brake light been wired into it?
What voltage and wattage is the brake lamp bulb
(or LED) and is it powered direct from the battery and grounded through the brake lever switch?
Alan