What is this on the firewall on 85 GMC?

[56weav]

Hello , upon my return both vacuum over electric switches on the firewall were not hooked up to vacuum , so both now are hooked up and receiving vacuum from the carb.
The distributor has the 4 wires coming out of the bottom and a vacuum pull on the distributor along with a knock sensor. The vacuum diagram does show a vacuum line from the carb to the distributor btw.
I drove the truck and I can’t say I tell any difference . I did fine anothervacuum leak and the cruise control is working better ( cruise was non functional when I bought the truck )