What the heck is this wire?
 

I was in the fuse box in the foot well whilst wiring DRL's and saw this extremely large wire tucked behind the fuse box. 4 core with the ends bare. It has direction arrows on it and disappears into the front door pillar at the side of the fuse box.
Any ideas?
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I can only surmise it may have been for an interlock-type device or a tracker. The harness doesn't look like it belongs in the car (as stock harnesses are wrapped in friction tape). Any way to follow it further?

I don't know what an interlock device is but there was definitely a tracker, I have removed various wires and a couple of little boxes but it is the size of the wires that surprised me, they must be at least 3mm each.
Never come across wires with direction arrows either

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The arrows denote which direction the electrons flow with Direct Current ( DC) :D

Interlock device is a breathalyzer that needs to be "satisfied" before the car can be started.