A note to add, my Haynes Manual has nothing on the cruise vacuum lines, or cruise control anything for that matter.
A four hour google search has brought up one photo diagram of another vehicle which shows my 3 port check but not the electrical device connected to it.
By the way, this is on a 1985 G-20 van, so this accumulator and 3-port check is mounted on the hood in plain sight and the cruise servo is behind the carb.