There are a variety of ways to wire up the serial port for the EFIS, and we can't say how your manufacturer did it.
The best thing to do is look around and under the panel for a 9 pin D-sub connector. If you find one, and it's female, chances are good it's for the EFIS. If you don't find one, they may have used a different connector, or may not have even installed one.
If you have the 9-pin, you then need to hook this to your laptop. If your laptop has a serial port on it, you need a serial extension cable to run to your laptop. If you don't have a serial port on the laptop, you need a USB to serial converter. You should be able to find both of these at any computer store or radio shack.
Ultimately, it was totally up to your aircraft manufacturer as to how they installed the EFIS, so you really should contact them.
