Do you know how to use an ohm/volt meter.
1)The frame may be insulated at your ground point.
I would measure from which ever ground point to the negative battery terminal
on the battery . The kit I got took both wires are attached right to the battery lug.(not a Technic kit for power)
I hope you are using a fuse on the + side .
2)If you are using a hot wire that plugs into the battery distribution block not all the slots are populated with blades/fusible links so if you plug into a no blade slot there will be no power. You need to inspect the slots to find one with two blades.
http://www.bawarec.ru/manuals/3er/e9...3er-e90-12.pdf
see page 6 item 6
Be sure to measure for a low resistance ground and hot
connections and voltage at the amp terminals that make
sense before applying power.