here is another idea.

print these https://www.thingiverse.com/thing:2519593
they will also provide good noise dampening.

now you have space underneath the delta where you can mount the duet without interfering with the motors.

There's been a few mentions of node red, maybe you can find something helpful here.

https://forum.duet3d.com/search?term=node red&in=titlesposts&matchWords=all&sortBy=relevance&sortDirection=desc&showAs=posts

@droftarts Thanks. Just checked. It's the blown fuse.

sorry i just realized how the setup is one.

are the switches NO or NC?

i would try to wire them in parallel and use M558 P5

they will need to be connected to the z probe port.

but a construct would allow the printhead to move. this would not be beneficial for the print quality.

@hamiltonprops From re- reading your OP, you say that the temperature drops 20 degrees within a second or two. That would indicate it's not a "real" drop in temperature but rather a drop in the indicated (measured) temperature - unless your hot end has an insanely low thermal mass. So, yes I go for some sort of cross talk or electrical "noise". Are you sure you haven't got a bad crimp on the thermistor wiring somewhere?

@dc42 Thank you, that pointed me into the right direction.
I tried to use a different circuit for the Heatbed as the Main Vin of the board has a 6A Breaker.
The Heatbed is now switched externally by a separate Mosfet, this works perfectly, also directs some of the High Current Stuff away from the Duet.