Hi Tom and
to the forum.
My preference would be to put a cosstube along the frame to give it a strong backbone and then run the cables along it in a more direct route. Then you could fit a seat and some footrests for a more comfortable ride.
Alternatively, you could use a length of 8 core network cable to extend the front harness as shown here:
Try and make sure that the joints will end up on the part of the harness that can be strapped to the frame for additional support.
Judging by the length of the scooter, I'm guessing it will be used for carrying more than just one person. If this is the case, I would be very concerned about the strength of the welded joint on the steering tube and I would strongly recommend welding some triangular plates
(or a piece of box section) between the steering tube and the diagonal part of the frame to strengthen the joint as shown here:
I think you should reinforce this joint anyway, just imagine what could happen if it suddenly failed while you were travelling along at 20mph.
Alan