[V]

Matt, now put a piece of cardboard inside the trans tunnel(to cover the trans, and use rustolem spray paint, like flat black grill paint(high heat) and spray from the inside of the car into the hole. That way you can get some better coverage on the inside of that void in case you get any water intrusion after you figure out the plan to plug the hole.

You could seal the hole in several ways now, other than a large round grommit/gasket. One would be to make a square plate with a hole drilled in each corner and a slot halfway down the middle. drill 4 holes on outside the trans tunnel around the hole which line up with the 4 holes on the plate. insert wiring, then slide plate over wire(through slot) and use 4 machine screws and bolt plate in place after using seam sealant. You could also put the plate on the inside, and re-pin connector through it so its one with the harness(use small grommit then). then cut a horizontal slot on the interior hole so you can slide the plate in laying down, then flip it up to line up with 4 inner drilled holes and then bolt in place.

I may have lost you in the progress of that last paragraph. lol, ill draw up pics if you want.