Hi Luke, Kia called the BCM an ETACS unit in the early vehicles. It's above the brake/clutch pedals.
The relay you have is controlled by the ETACS via the tail-lamp cut relay:
TAIL LAMP AUTO CUT
(1)
With the tail lamp switched ON, if the ignition
Is switched OFF and the driver's door opened, the tail lamp should be automatically turned OFF.
(2)
With the ignition switch ON, if the driver's door is opened and the ignition is switched to OFF, the tail lamp should be automatically turned OFF.
(3)
When the tail lamp is cut automatically and the tail lamp switch is turned OFF and ON, the tail lamp illuminates and auto cut function is cancelled.

The relay is earthed through the ETACS unit, into the switch (the switch is on the earth path) onto the earth via a multi-wired joint called JM04 (the upper of 2 main joints). This is behind the dash/radio as is the earth point.
ETACS units don't like damp......

Unfortunately, you haven't included an email address, so I'm unable to send you any wiring diags or files.

Tony