Fixing DIY Cool suit leak

For the hole where the wire goes from the pump, through the cooler body, to the power source, water keeps going through that hole no matter the  type of seal I've used.  I used some silicon caulk that was used for the other fittings, but it came apart easily - still working great for the other fittings.  I tried using some bath tub caulk and it held up well, until the cold water made it brittle and it broke apart.  Any suggestions of something that will hold up under race conditions?  The wire isn't held in place (to minimize vibrations) either on the inside or the outside of the cooler.  I'm sure that's part of the problem, all that unnecessary movement.

TIA.

Still looking for suggestions.  Guess I'm looking for something submersible and would hold up under cold conditions (and will work with plastic).

Windshield butyl.  Also restrain the wire somehow.  You might also consider running the wire somewhere that's not below the water line.

I've done a cheap bulkhead fitting by using a gromet with a bolt through the center, with ring terminals on both sides of the bolt.

I ran the wires through a small pi3ce of tubing.  That tubing I shoved through the hole I drilled through the cooler.  (Hole slightly smaller than the hose).

Then, I just used water pump rtv on the wires where they go through the cooler.