I have a 1998 5.2L B1500. It is a mess! I had two vacuum lines disconnected, one is in the first picture, I found where it went. There is another white one running alongside it, with no apparent connection. Anyone know what it is and where to look? Vacuum info is confusing since manuals leap around.

A black line attached to this on left side of engine

Three lines come out of the bulkhead near master cylinder - 2 black, 1 white. The white one is unattached

 

All those lines have to do with your hvac system as in the flappers that control where the conditioned air goes and recirc activation. Mine has several more. Maybe they cleaned up things in later years.

That black one looks like it has been kinked and may need replacing.

 

Diagram is for 1997. Speaking 1996, I think the black line picks up engine vacuum from the intake manifold. The vacuum reservoir is #8. I think your white line is paired with another and goes over the heater box to the vacuum diaphragm behind the passenger headlight.

 

I think your white hose is the one to the Heater Control Valve. That vacuum-operated valve is considered to be part of the HVAC system, so it's not shown on vacuum diagrams! If I remember correctly, it's just an on-off valve (not modulating), and it shuts off the flow to the heater core when you select "max A/C".

The valve may still have the other end of the white hose attached. It is under the hood on the passenger side, close to the heater core, and looks like this:



On my '98 3500, the ex-white plastic hose was in several separate pieces; I replaced it with some I found on Amazon (teflon, I think).

Hope this helps!

 

It would be nice if the diagram would be color coded. I find a lot in the manual that leaves you guessing.