I can confirm that my 57 1.6HDi has a similar redundant spur from the loom in the same location.
As for your STOP lamp, I would suspect the brake fluid level first. If you unplug the connector at the top of the master cylinder reservoir cap and the STOP light goes out then this is the cause. If it is the brakes the light that illuminates when the hand brake is on should also illuminate though. The fluid level sensor is very sensitive, as said in previous posts, I would check the rear slave cylinders first, assuming you are on drums at the rear. Look for fluid around the bottom of the back plates.