We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember "The Medway Handyman"
saying something like:

I assume some kinda electronic gizmo senses the load and does the switching.

Can you buy said gizmo to fit to an existing vac?

Get one of the vacs from Lidl/Aldi next time they're in. I was using
mine that way to collect concrete dust from 14 double socket holes and
it was tremendous the way the dust got sucked in as I worked.
--

Dave