Do you actually have all the wiring already or are you just asking preliminary questions? If you at least look at the wires and the manual you will see where the wires from the derailleurs connect to the battery. There are junction points that get sealed to make them water tight.
Look at the pictures of the S3 as it is the cleaner build of the two. The P3 was routed internally with an external harness as that is what the customer supplied. Using an internal harness like on the S3 is a better setup but not appropriate for all setups. Again, please look at the wiring and the manuals for them so that I can answer your specific questions on what you need to do, some of your questions will be answered by looking at the harnesses. It makes a lot more sense if you can look at the harness while you read my response so you know exactly what I'm talking about.
Unfortunately I can't take additional pictures for you as the customers have picked up their bikes and are out enjoying them.
.
-Darrell
Look at the pictures of the S3 as it is the cleaner build of the two. The P3 was routed internally with an external harness as that is what the customer supplied. Using an internal harness like on the S3 is a better setup but not appropriate for all setups. Again, please look at the wiring and the manuals for them so that I can answer your specific questions on what you need to do, some of your questions will be answered by looking at the harnesses. It makes a lot more sense if you can look at the harness while you read my response so you know exactly what I'm talking about.
Unfortunately I can't take additional pictures for you as the customers have picked up their bikes and are out enjoying them.
.
-Darrell