Hobbs Switch wired into car, what is its purpose?

[biddie_fiddler]

So as I have mentioned in previous threads, I am currently in the process of a turbo upgrade which includes an external wastegate setup.

 

My brothers car already has this setup so it makes for a perfect car to learn off of and replicate how its done. I thought it was plumbed up exactly like the factory wg was (TLDR, it is) but I noticed a tee-off on the boost reference line that comes straight off the compressor housing.

 

Following the tee, it led me to what I now know is a Hobbs Switch.

My brothers car has a process west surge tank, and I believe it has 2 pumps fitted to it. But this has me thinking, what is the Hobbs switch used for? I'm guessing it may have something to do with the surge tank as a form of staging the pump, but that is my only guess. The hobbs switch is connected between a relay and ground, so I'm thinking its used as some sort of trigger switch for the relay, hence why I think it could be for the surge tank.

What do you all think this setup could be used for if not for staging pumps? 

It had me stumped for a while because I had no idea where the tee was going to, took me a while to find the hobbs switch 🤣

 

Here is my crappy reference as to how it is connected to the boost reference

 

[El Andrew]

Yep, is usually for pump staging. Will switch on the second pump once a certain boost pressure is reached. Saved having both pumps running all the time and also less fuel circulating and heating.