Hello Jacques,
if you look at the cut-outs in the rear mudguard (or better: the plastic battery protection shield that sits behind the battery, screwed to the frame), I think it is quite obvious how it starts on the right side: From the top of the brake master 45 degrees front left, between frame tube and the plastic cover. Then over to the other side, exit at the equivalent place and down to the swing-arm. left of the swing-arm, you guide it down to below the swing-arm and from there to the rod that connects the caliper-holding plate with the frame. zip-tie it to that rod until it reaches the caliper.
that is at least how I did it.