m_c,
I think you're right, I did suggest Dan check for 24v on the mill input to check. It's the lack of a pull-up on the input side that is most important here.

For those who might worry about it, two pull-ups in parallel will not cause a problem as long as the total current through the relevant transistor when on is within limits, so adding an external resistor for testing purposes will not harm anything. 2Kohms per volt (gives half a milliamp of current) is a good rule of thumb.

Kit