[Kevin Sevcik]

Your code to write to the serial port should work, though I recommend you pick Write or WriteLine, and not try to use both. There's a large number of reasons why this might not be working for you, though. If you don't have the communication parameters set correctly, you can end up receiving but sending gibberish to the GPS, or not sending anything at all. You also might not be sending the appropriate end of line characters in the appropriate sequence. Common options are "\x0A" (new line), "\x0D" (carriage return)(Ding!), "\x0D\x0A", and rarely "\x0A\x0D". Your GPS might use more exotic characters, however.

If you have it working over Tera Term, make sure you have ALL of the communication parameters the same, and then find out what end of line characters it's using. Once you make sure you're doing everything the same as Tera Term, it should work for you.