6.2 Secondary Filter Question

[Burbinator]

I'm currently working on my '87 Suburban 4x4 with a 6.2 diesel. I'm going to yank the secondary filter for a needed upgrade. As you all know, the secondary filter on the 1987 to 1991 models have three connections to the wiring harness:

1. The WIF sensor connector down at the bottom right near the water drain valve
2. The fuel heater connector up top
3. The Restriction switch connector on the bottom left

My question is simply this: what does the Restriction switch do?

Here's a diagram of the assembly for reference.



Thanks for the help!

[Subzilla]

On these years of 6.2's, this is the only filter unless somone installed another filter. The 82/83 models had the primary/secondary filter set-ups from the factory.

The restriction switch measures when the filter is plugged up or restricted. I can't tell you how it works.

I've seen the housings for sale from time to time on Ebay.

[NH2112]

The restriction indicator switch is nothing but a vacuum switch that senses differential pressure. When the filter is clogged there's a pressure drop and this closes the switch, turning on the WIF light.

I'm a big fan of using the stock Model 80 filter as a primary, and installing something like a Racor 445R w/2 micron R45S as a secondary filter. Underneath the snorkel on the radiator support is a great place for one.

[Burbinator]

Thanks! Mystery solved about the Restriction switch!