First, start it on both ignitions. Or better yet, just start it on the P-mag. If it is a new P-mag with version 40, it will fire at 4 degrees past TDC until it sees 200 RPM. At that point, the timing will move back to the right place.
If you do not have V40 firmware in your P-mag and continue to start it on the magneto, your P-mag runs a VERY good chance of losing its timing mark. Firmware V40 solved this problem. (Older P-mags can be upgraded to V40. Contact Emag for details.)
If your timing is supposed to be 25 degrees, install the jumper (pins 2 & 3), which will force it to the A curve. If your timing is supposed to be 20 degrees BTC, you are going to want to adjust the timing map with Emag's EICAD program.
As for the wiring, make sure the ground wire coming off P-mag pin 1 is grounded to an engine case bolt. DO NOT ground it on the firewall or any other place!
Pin 5 needs a 12 volt power supply. Mine is protected by a 5A pullable breaker. Pin 4 is your P-lead and is what you use to "ground" the ignition, same as a P-lead on a traditional magneto.
How you wire and test your P-mag is up to you. Mine are wired with a three way toggle switch and the aforementioned 5A breaker. In my configuration, down is grounded and unpowered, the middle position is ungrounded and unpowered, and the full up position is ungrounded and powered. This allows me to check to make sure the internal generator is working properly as part of my preflight.