How to approach soldering a serial connection?

[Mangix]

I recently bricked my pogoplug by updating the bootloader to the most recent one on this forum. I am confident however that the bootloader works but is somehow misconfigured. I base that on different behaviors when having an SD card plugged in and without. Basically the LED stops blinking with one in.

So how should a serial connection be attached? I'm thinking a standard pin header but the holes are not space properly and are not empty. Would I need to find a cable and route it somehow?

[Guidobelix]

As you mention an SD card, I assume you have a Pogoplug 4.
If that is true, then you can find a good how-to here:
Pogoplug V4 Disassembly and Attaching Serial Cable