Link to a good wiring diagram for pins and good reference material for speaker swaps~
http://www.dziedzic.us/wpc_speaker_sound_info.html
Where you mount the "L" pad is personal preference. Some like it near the coin box where you can adjust it by opening the coin door. I prefer to mount it in the head box / upper right corner. HS2 has an aux board in the upper right so on mine I mounted it mid ship or a little lower. Once you have the balance adjusted I rarely touch the "L" pad again.