EGR Vacuum Line?

See http://www.veryuseful.com/mustang/tech/engine/images/88Stang5.0Vacuum.gif

Or

http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

The EGR gets a white line connected to it. The 4 hose coupler has one blank position with no connection.

The back side of the 4 hose coupler has red tube the couples to the white tube that goes to the EGR. The red tube comes from the output side of EGR vacuum regulator

The green tube goes to the coupler and then connects to the intake manifold. This line has been changed on mine, and I do not know what the orginal color was for the line that connects to the intake manifold. The green tube connects to the input of the the EGR vacuum regulator.

To add a bit to jrichker above, intake manifold vacuum does not go directly to the egr valve. Manifold vacuum goes to the egr vacuum regulator/switch (located on the firewall). The output of that switch gets connected to the egr valve. The computer tells the switch when/how much vacuum to deliver to the valve. Vacuum when delivered by the switch overcomes a spring/diaphragm in the egr valve causing it to open and admit regulated amounts of exhaust to the intake.

The white line in the center goes to the thermactor diverter valve. Not needed in this case. There are two long black lines. One goes to the rear of the intake to one of the small vaccum ports, and the other goes the smog pump. Cross those out. There should be one shorter white line left and that goes to the EGR. Follow jrichker's post on how the coupler plugs together and you'll have it. If this is still a bit confusing, I'd suggest going to a junkyard and seing if they have a 5.0 that hasn't been mangled in the front. Lift the hood and see what it looks like. The yard I use let me have the coupling for free (my lines were all broken) and I found out how to run it to boot. Just carry a sheet of paper to write down what you see.