I put my plotter right at the helm where it does the most good. (photo attached) Cheated, in that I just dropped down to the engine control pod and picked up the power for the plotter right in the pod. (I did fuse the plotter separate of the engine / instruments that were factory installed) When I installed the Radar upgrade, I had to pull more wires through the tube, (it is getting pretty tight in there) and went all the way back to the main panel for power. As I noted above, all depends on where you plan to put things. I mounted the junction box, and pulled all the wires for the plotter / radar interface under the steering gear. (photo attached)
Hope this helps - Russ