[GreenKeys] Four-prong wiring question on M19s...

[Jim Haynes]

On Thu, 25 Jun 2020, E. wrote:
>
> with the ohm meter to try to trace things out.  To recap, the 19 has the 
> rare four-prong AC plug and the table has two four-prong jacks - one in

But it isn't rare.  Practically all M15/19 bases have that four-prong plug
for AC in (two wires) safety ground (one wire) and AC that has been 
through the power switch on the base, so that switch can control other
things plugged into the electrical service unit.