What Do You use to make neat/professional wiring in dummy units?

Have all components mounted, either tightened down or temporarily, as required.  Then, run all the wiring as needed.  Keep the wiring in a neat bundle.  Cut the wire to reasonable lengths before attaching.  Be sure and allow just enough excess length to allow the component to be unfastened and manipulated properly for inspection and observation, without having to remove the wiring first.  Use twist ties or a little tape or small Velcro straps to aid in tying up the wire looms.  Zip ties are fast and easy, but unfortunately almost always have to be cut if you ever need to remove them.

Any wires that attach to the trucks must be allowed adequate length to move and flex as the truck turns from full stop to stop.  Try to run the wire so there is as minimum amount of wiring flexing as possible when the trucks turn.  This will allow much longer life for the wire, instead of breaking prematurely from constant flexing of the truck.

If you have to run wiring from the shell to the frame, be sure and allow enough wire length for both the shell and the frame to be comfortably separated while lying on the work bench.  Also, try and have a plug-in connection from the shell wiring to the frame instead of hard-wiring the two together, so you can completely separate the two if need be.

Once again, the best thing you can do is make sure you don't have wires any longer than need be.  Wires too long contribute to the "rat's nest" look, because the excess has to be bunched up and wadded into nooks and crannies under the shell.  Not very professional looking.

And what about the power lines coming in from the roller pi k ups? Cant have 5- 7 different wires connected to just two wires