I checked my factory built VW based car this a.m. and basically confirmed the info I posted previously.
A large blue wire connects to the same terminal on the starter that the + batt. cable connects to.I found what I believe to be the other end of this wire connected to the right side of the ampmeter as viewed from behind the dash.This is the only blue wire of this size under the dash and I think this would be your wire 23.
Two red wires of the same size connect to the left side of the ampmeter and go to a junction block [not the fuse panel] which serves connect wires from the front,rear and under the dash.,This would be your wire 15 if I am correct.