Manual transmission clutch switch

[Cudalbs]

My car has never had a clutch switch hooked up while I have owned it. Just a 2" cut off piece of wire coming off the switch. So today I went out to wire it up and I'm not quite sure I understand how this thing works. The wiring diagram shows this one wire running up to the ground on the starter relay. I am certainly not and electrical expert, but I don't understand how that makes this switch do its job. If it runs to a ground, couldn't it just run to any ground since all the grounds are common? Like I said, I'm no expert so maybe someone can explain how this works.
Thanks, Mike

[Roadman]

     The ground triggers the starter relay. 

[GoodysGotaCuda]

The starter relay under the hood needs 12v and a ground source to actuate. The ignition switch provides +12v in the "start" position, the ground will come from the clutch switch when it is depressed.

[Cuda Cody]

    

[Cudalbs]

Aahhhh, I see now. I have a ground already coming off of the relay that I will need to disconnect and then replace with the wire coming off the clutch switch. I feel pretty dumb now that I see what's happening. Thanks you guys, sorry to waste your time on that one. 

[Roadman]

Aahhhh, I see now. I have a ground already coming off of the relay that I will need to disconnect and then replace with the wire coming off the clutch switch. I feel pretty dumb now that I see what's happening. Thanks you guys, sorry to waste your time on that one. 

                    Not a prob, that's why were here.   

[71GranCoupe]

Aahhhh, I see now. I have a ground already coming off of the relay that I will need to disconnect and then replace with the wire coming off the clutch switch. I feel pretty dumb now that I see what's happening. Thanks you guys, sorry to waste your time on that one. 

I am sure others out there will benfit from this good question and the great answers. It is always a good refresher as well.  It is called teamwork.