Coolant sensor and Fan switch are 2 different things.
SENSOR mounts on driver side engine block and sends input to the ECM.
Fan SWITCH is located low on the driver's side radiator.
SENDER is located at the driver side rear of the head and sends signals to dash gauge.
The heated intake manifold likely had to do with emissions in all types of weather.
Fuel and air traveled together through the manifold.
I only experienced "icing" on my Nissan Patrol with an aluminum one barrel to two barrel carb adapter. The mechanical fan blew a ton of cold air on the adapter and caused issues. My Redneck solution was wrapping the adapter with ethofoam insulation held on with zip ties. Worked great.
MPFI only air travels through the intake.
I say try it. Couldn't a guy just loop the hoses together in the name of science?
Does the electric fan come on during this "overheat" time without activating it with the AC?
Still have the coolant bottle on the passenger side firewall?
Have you performed gogmorgo's suggested test on the clutch fan?
Do you have a temp gauge or just a warning lamp?
Likely unrelated and you have more than one issue.
Turn signals and wipers not working is likely a burned brown wire at the ignition switch on the column. Blower motor usually doesn't work either.