I would pull the control as pictured in the link I provided. Find the rotary vacuum switch. Identify the supply vacuum hose. If you can't find where it comes through the firewall bore a hole bigger than the hose find a rubber grommet insert it and run a new hose through the grommet hook it up test. If working properly caulk the opening through the firewall. I've run a new wire this way. It lasted until I sold the vehicle.