Dave, on all SD's from '81-'85, the two vacuum switches on the top of the valve cover serve to operate the EGR exclusively.

They have no direct operation or effect on the transmission shifting.

I've recommended to everyone who has these engines to remove all the Tecalan lines that lead to and from the black box.

One line is the supply vacuum.........one line is the vent.........and the third line leads to the thermo vacuum valve in the thermostat housing and then onto the EGR valve.

These switches frequently leak and have an undesirable effect on transmission shifting however, they have no direct function reagarding control of transmission vacuum.

Please realize that older engines, prior to 1981, will likely have a different configuration.