how does a hood sensor work?

More specifically, how do you wire it?  Do you just take the wire from the brain for the senor and plug it on the bottom? Then where it mount it is where the ground is?

Thanks for your help

Yes, they typically ground through their metal body.

If you look closely, you will see the entire body is metal.  The plunger itself is plastic.  On the end of the plastic plunger there is a metal connector for your wiring.  When the hood pushes the plunger in the metal connector is seperated from the metal body.  When the hood is open and the plunger springs back to its normal position the metal connector touches the metal body it sends a ground signal to the alarm brain.

Basics?  Ha!

In a year from now he'll be asking how murcury switches work so he can replace the rusted out hood pin!

I never did find a way to mount them where they would survive an Ohio winter.