magnetic reed switch to negative trigger?

Hi, I want to put a magnetic reed switch on my 2002 Ford F-150 bed cover - it's a tonneau (however that's spelled).  My alarm is a Viper 560xv 1-way remote start.  From what I've read on here a reed switch is the way to go.

I'm already using the negative trigger (green from Viper) for my doors by connecting that directly to the pink/light green wire at my headlight switch.  I do have an unused violet (+) positive zone 3 door trigger wire on my Viper, plus an unused blue (-) negative "multiplexed input, zone 4".

Question 1: To wire the reed switch, do I just connect one of the 2 reed switch wires to the blue (-) multiplexed input on my Viper, and the 2nd wire from the reed switch to ground?  Any relays needed?

Question 2: What's a good reed switch, and can I buy one at a major retailer, like a Circuit City or a Radio Shack?

Thanks!