MK2.5 Brake Light Wiring Diagram?

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A few months ago, I clipped my spoiler on my shed's shutter while reversing out. I pulled the spoiler off and ripped the brake cable in the spoiler. I'm left with two ripped wires coming from the car and two loose cables with the brake lamp connector on the other end. I've finally gotten around to repairing this.

What would be the best way to fix this? I guess I could figure out the polarity of the cables coming from the car by stepping on the brake and using a multi meter. How would I find the polarity of the loose torn wires connected to the lamp plug? 

I've pulled old spoiler off and popped the harness protector off the hatch to expose the wires. I only have access to a few inches of the torn cables. I can add photos too if that helps.

Thanks guys.

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Just to close the thread:

 

I didn't bother with my multi-meter. I took the old spoiler off, passed the ripped brake lamp cable through the boot (I worked in the boot, covering the boot with an old curtain. and undid the grommits so I could get access to as much of the cable as I could. The loom had tape around it (inside the boot cavity) that took a while to tear in order to separate the two cables I was interested in from the rest of the hatch light loom. I stripped the ripped ends of the two ripped cables. Next, I grabbed the loose torn brake-lamp connector side of the cable and wrapped the stripped cables to those in the car. I randomly chose which cable to wrap with which (from the two cables of interest),  I'm guessing polarity doesn't matter but I still wanted to check. Next, I plugged the lamp into the connector and left the lamp dangling above my backseats. I turned on the car and checked if the light worked by pressing the brakes, and it did. As another sanity check, I had my phone record the back of my car to make sure my primary brake lights were still working, in case I damaged a cable, messed up the grounding or had blown a fuse.

 

Once I knew everything worked, I unplugged the lamp and unwrapped the wires. I passed some heat shrink over the cables. I rewrapped the cables together and soldered them together. I don't have steady hands and soldering with clamps on a table is messy for me on a good day. Safe to say you should cover your lap with some old material if you don't want molten solder dripping onto your legs.... Also if you're doing this, pay attention to the shrink tubing, I accidentally shrank some as the copper wires conducted heat to the tubing. I had to insulate part of this cable with electrical tape instead. 

 

Thats pretty much it! I passed the whole-again cable back through the boot and through the spoiler pass-through. I refitted the grommet/plugs and works perfect now.