What's this vacuum/pressure switch near wiper motor?

[rickshaw]

Recently bought an 86 SVO, head is off to BoPort. Otherwise cleaning up and painting stuff under hood. Found this switch tied into vacuum hose, see photo. Checked my Ford service manuals and doesn't show up on any wiring diagrams. Switch is normally closed at atmospheric press and opens under vacuum. Somebody knows.

[svono50]

Ah, that is your fuel pump NVH switch...at least that is what I am calling it. It is a pressure switch that drops supply voltage to the fuel pump to 9V in order to quiet it down when idling or high vacuum cruising. The stock switch closes to give full system voltage to the pump around 5" vacuum up into boost. You can technically remove it and jumper the harness plug if it starts acting up on you. Mine was not closing, so I could only achieve 60psi fuel pressure closing off the return, which is not a good thing.

[rickshaw]

svono50, thanks. Pretty sure I would not have guessed its purpose. Will test this later when engine is back running.

Also, I added an adjustable fuel pressure regulator, is the Ford, original Bosch, regulator set at 39 psig? To set this with engine running, I'd disconnect the vacuum line so it sees atmospheric pressure? Or I could do this without engine running if I can run the fuel pump by grounding one of the pins in the EEC test connector? Probably will try to do the latter so I can drain fuel from the tank so I can change the fuel pump to the 255l/hr pump

[svono50]

The OEM regulator is set to 39psi 'static' pressure. A former master Ford tech explained that the specified pressure is actually w/o the engine running. So, I have been setting my 'base' fuel pressure this way ever since. I have a Kirban unit on mine for reference. To do that, you jumper two of the pins on the EEC self-test connector with the ignition switch in the 'run' position and the pump will power on. I know I posted up a diagram on here of which two pins to jumper, but I found that out on the interwebs, so I can't take credit for it. I made a short jumper wire with two crimp-on male spade fittings to plug into the EEC test connector, very easy.

That pressure switch is also adjustable, just as another nugget of info. The adjustment screw is located between the electrical blades on the harness side. I played with a hand vacuum pump to actuate mine when I was trouble shooting it, which is why I know the approximate switching point. I have yet to cut my switch open to see if the contactors have worn out or just what happened, since you can clearly hear it still actuate.

[rickshaw]

OK and thanks. Found this diagram.

[svono50]

Here is the diagram I found for reference:

Fuel pump test jumper 86-93 Mustang 60%.gif

[rickshaw]

OK, thanks