Need some help tackling a rear ABS wheel speed wiring harness replacement.

I have an idea where the rest of the wire leads to through the wheel well (into the trunk in the corners like where battery sits) but the rears don’t have a wheel well cowl on my model and year? It’s plastered with some sort of rubber material and even more where the wiring harness goes through the wheel well. Do I cut through it with something (what exactly do I use to open or cut it open or not?) to get the new wiring harness in to plug it up to the ECU bus in the trunk but most importantly what exactly is that rubber material? (So I can replicate the plaster and patch with that same rubber like weather sealing material)

 

Thank you. I can’t find anything online about the Gen 3 Prius repair for this exact replacement harness so I’m just guessing from here, would you use an exact knife for this if you were doing it, can’t imagine anything else that could be thin and sharp enough to work around the wire and not cut anything else on accident. I did find “universal” splice job videos but comments all say these harnesses are Ohm sensitive by 1 Ohm, I have no clue how much length of wire equals one Ohm. I might try it myself with some solder just will need to buy a solder and make sure it’s for electrical work but also an actual splice harness and not the full harness I already purchased only if find the other end in the trunk is a complete pain in the butt. I’ll update this thread for future users to search this exact repair as no one really here has done it.