If you use standard wire connector blocks, don't spray them with screwfix metal seal to stop water getting in - it goes all flakey, and induces rust
Also, when I put the extra wiring in on my boat for VHF etc.. I only put in wires that were thick enough for what I had at the time - when it came to installing the cigarette lighter socket, I had to replace just about all that I put in to start off with to handle the extra current.
If you have wires hanging around inside, zip tie them to something solid to stop them flopping around..... I found insulating tape lasts about 5 waves before coming undone
It's all fixed now, but I did it all wrong in the first place.....