The latest manual does have GPS connection instructions, but they are not model-specific since there a variety of units out there. With ANY GPS, you're basically looking for the serial output. This is a single wire and will be documented by the manufacturer of the GPS. You can download the latest installation guides here: http://www.dynonavionics.com/docs/support_documentation.html
For the Lowrance - first, you'll need the optional cable from them that has the serial wires. You'll want to connect the serial transmit wire from that harness to pin 22 on the D100's 25 pin connector (that pin is also continuous with pin 3 on the 9 pin PC serial connector, so you can connect there as well). You'll also need to makes sure the EFIS and the GPS share common ground.
