Batboard

So I have a UHF 450-512 CDM1550 LS+ that I absolutely love. I've installed it in the truck at work (Security). The boss wants to install a PA and Airhorn. I noticed that there is PA functionality in the CPS, so I enabled that in the codeplug just in case I was able to figure this stuff out. No such luck so far. A few questions:

1.) What do I short the PA Switch pin to (ground, +...etc) in order to tell it what to do?

2.) Will the pins for the External Speaker drive an external speaker directly?
2a.) How powerful is this output (Watts-wise)?
2b.) Will this be sufficiently loud on a vehicle?

Thanks for any help!
-Chris