I hope that it's ok I started another thread about this. The original was getting pretty long.
Anyway, I read all the threads and believed what people said but damn, I didn't think it was gonna be as loud as that!

Thanks for a good, cheap mod/addition. It's too bad they all can't be this cheap!
I installed it this afternoon/evening. I had trouble making a good connection. I eventually ended up cutting the two conductors off the HD connector and crimping female connectors onto them then I crimped male connectors onto the wires coming off the siren. ( Damn, those wires on the siren sure are a small gauge!) I attached the siren in place with industrial Velcro.
I tested it once I finally put these connections on and wow.
After I tested it, before I buttoned everything back up, I crimped male connectors onto the short lengths of wire I left coming out the back end of the HD connector so in the unlikely event I buy the HD siren, I can hook everything back to the stock connector.
I tested it again after I put the side cover and saddlebag back on and it was still just as impressively loud.
So all in all, a really good mod/addition. I'll feel a more secure leaving my $21K toy unattended now. Flashing lights wouldn't scare somebody away but that siren surely will!
HSP