Old trucks gaf. Idk why you'd think otherwise. Most plugs are not expected to be submerged. If you go so old that there's no powertrain electronics (which tends to also predate water resistant electrical connections), water is still going to accelerate corrosion at connections, especially chassis ground taps. Submerging it is how you ask for undiagnosed gremlins. Sounds fine for a trail rig, doesn't sound fine if you still want your legally mandated lights to function.

Plus, it's especially problematic when you get water inside the cabin. Tons of unprotected connections in there.