I am restoring a 1986 Dodge D150 truck with a 225 in engine. It is equipped with a dual vacuum solenoid. It has four vacuum connections on one side and two on the other. One of the connections has no vacuum line (white arrow - that is currently plugged). Should there be a vacuum line connected to this vacuum port? I have studied the parts book and the service manual and cannot find a reference to the side of the dual vacuum solenoid with the two vacuum connections and the two electrical connectors. Should there be a Y connection from an intake manifold source for this connection? See photo below.

Looks like one is your air switching solenoid valve, and the other is your EGR control solenoid valve. Note some solenoid ports are open to atmospheric, but have a foam filter pushed over that port to act as a filter. If the filter disintegrates over time, someone unfamiliar with the system might replace it with a cap. Check this diagram and see if your vacuum system matches up, or determine what's been disabled and/or removed.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

just a tip i have a 85 D100 if/when you replace the brake booster vacuum line be extremely care full When i replaced mine the multi port aluminum hose barb broke off flush with the intake manifold very annoying. upon inspection the casting was vary porous it had bubbles 3/32 in diameter.
good lock

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85 d-100 HEI 2BBl
06 Toyota Corrola

Side note to early 80’s engineering, or what were “Theyâ€￾ thinking department:

Dan, that plumbing nightmare looks not unlike the vacuum line rat’s nest under the hood of my 1982, 2.6 Hemi equipped Lebaron. Yup, the 2.6 L Mitsubishi diesel truck engine that was converted to gas, equipped with a funky reed valve pressurized exhaust recirculation system including a third “Jetâ€￾ valve per each cylinder and counter rotating balance shaft, turned sideways, and stuffed into many a K Car and fork lift. Oh yeah, the dreaded Mikuni carburetor, oh boy, what a joy that marvel can be. Thank God fuel injection was just a few model years down the road, luckily all of her under hood plumbing diagrams are in pristine condition.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC