Well, knowing what I know about wire harnesses, I personally would never submerge my cars wiring harness in any liquid. Except maybe isopropyl alcohol, that has a tendency to flash off fast. Wire tends to act like a big sponge and will suck up the liquid and hold it for a long time (wicking). Most wire harnesses produced in industry are tested (insulation resistance, dielectric withstanding voltage) for that and other non-conformances before being put into service. Separating the wires and wiping the outside of the insulation with alcohol and a rag is the way to go. JMO.
