What is the purpose of the fuel suction switch at the filter head?

[mattplumber]

Mines been unplugged for a long time. Runs fine without it. Was just wondering what the purpose of it tis............

 

[dsltech83]

Turns on the fuel filter light, lets you know when it is restricted.

 

[hairyboxnoogle]

The one on the bottom of the filter, that is a water in fuel sensor is it not?

 

[dsltech83]

The one on the bottom of the filter, that is a water in fuel sensor is it not?

Correct, the one on the bowl on a 7.3 filter head is the WIF light, the restriction switch is on the head itself, on 90 and up I believe(not sure though).

 

[hairyboxnoogle]

Ok i was jw, as in my 79 i hooked the WIF circuit to my cluster BRAKE light, and the GPs to the seatbelt cicuit. I was curious as even though ive had water in my fuel its never came on, and i know the circuit is functioning.

 

[icanfixall]

Thats what the switch does. It tells you the filter has a restriction and the injection pump is pulling so much fuel that the vacuum is present now in the line from the filter to the ip...