There should be a line from the intake manifold to the fuel pump, and another one from the pump to the wiper motor. The pump doesn't provide all the vacuum- - - -it just enhances what the engine produces. If there's room to put a reserve tank somewhere under the cab, etc., it might not even be necessary to run a dual action pump. A piece of 4" PVC pipe a couple of feet long with caps glued to both ends makes a very good vacuum reserve tank and it's easy to hide along a frame rail. Just use a one-way check valve like the one for a power brake booster to keep the vacuum in the reservoir, and another hose to the wiper motor.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!