I second sailingdog. The only reason for soldering wires is because marine grade tinned wire is not being used, and it is an attempt to protect the copper wire. Tinning the wire yourself also leaves it stiff and subject to stress and vibration fatigue. In addition, standard pvc insulated wire is not waterproof. A quick immersion in water (I don't know where from, maybe your bilge
pump is shot or you're sinking) could very quickly open a live wire internally.