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I believe my windshield wipers are plumbed to the auxiliary vacuum pump on top of the fuel pump, but I will verify this tomorrow.
The aux vacuum pump is in series between the wiper motor (and vacuum antenna if you have that option) and the intake manifold. In normal use the manifold provides all the vacuum and because it is stronger than pump vacuum the valves inside the pump are kept open and pump just acts as a pass thru. In cases of engine load or wide open throttle when manifold vacuum is minimal or non existent the valves in the pump start operating and the pump takes over and provides vacuum to the wiper motor at a reduced volume to keep the wipers moving at a slowed speed.
On a 48-50 there should be port at the top front of the manifold and via a fitting and curved tube enters the fuel pump vacuum section at the front. Another tube exits the rear side and follows the block to the firewall area where via tubing and hoses vacuum reaches the wiper motor. If the vacuum antenna is present, a tee in the wiper hose near the motor feeds the valve for the antenna.
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