1984 GMC C1500 trans converter vacuum switch and ignition t

What is a trans conv vac switch. The emission hose from the egr tvs connects to this vac switch than it turns into an two prong connection. The ignition timing vac switch also comes from the egr tvs and
also turns into a two prong connection. There is an-
other vac switch that goes from the efe tvs that connects to another two prong connection that goes to the transmission control solenoid (TH700R4).
What is the purpose of each switch and how do we check for proper operation? I am overhauling engine and replacing vacuum emission hoses but have not found any info on the above items that might need replaceing. I have also found vacuum dagrams and electrical diagrams but no info on the above.
?LLOST WITH NO INFO.