Let me disagree. The strobes will have the same number of wires, as the signal source ie the camera is the same. If for whatever reason one strobe runs with fewer cable, being that it doesnt cater for TTL, then it is just a matter of figuring out which is the redundant wire. You haven t mentioned which camera make you are using but there are ample web resources that detail the hot shoe wiring, for different makes and models.
As for leaking the splice. Providing it is done correctly a splice will keep water proof for a 100m plus if you are using 3M self amalgamating tape. This would be the most economically way. Also a soldering iron and self amalgamating tape it an essential part of my tool kit, with it I can seal nicks in cables or salvage cords should they fail. Kept me shooting many a time.
For a more professional finish you can use a mold and 3M scotchcast, which will produce a flexible rubber cast. Prepared and set correctly this will stay water tight to 2000m plus, probably more, though I have never tested beyond that depth.
I heartily advise you to rip stuff apart and solder them back together in a way that works for you.
If you have any questions let me know.
Erol