Smoke coming out of defrost vent on 1979 ford f150?

After we changed the distributor and ignition switch it started doing it. My windshield has been fogging up but its on 50 degrees out. Heat and defrost are all off so it should not be doing anything.

Strange. If putting the system into recirculate mode stops the smoke, you'll know that it is being drawn in from the engine compartment.

which would make me think that somehow you've accidentally moved something like a spark plug wire so that it is laying on the exhaust manifold

The heater core in your old van has a leak. It's not smoke, it's steam.