disintegrating electrical tape under hood undercarriage

It is best to remove all damaged tape and check for exposed conductors through the chewed insulation. I have this problem on the RAV, where mice are constantly chewing on the A/F sensor insulation as well as subsequent wrapping with electrical tape -- and I get ABS/VSC code C1201 when they succeed in causing a short, for whatever reason.

If there was harm in getting water inside there, you would have found out immediately. All wiring and connectors inside the engine compartment are supposed to be water tight, at least splash proof anyway.

 

The best solution is to go to your local cattle feed store and get some rat poison. Put the rat poison under the car. Keep pets away from the poison unless you don't want them either. Put a half filled bucket of water near the car. Come back the next day and you'll find drowned rats/mice in the bucket. Sorry if this offends your animal sensibilities but rats/mice can wreak havoc on a car.

Then do your repairs with the confidence that it'll probably be days if not weeks before more rats move it.

 

Toyota probably used electrical tape because it was the cheapest solution. I would use tie wraps.

I had a rat chew on ignition wires on one of my pre-Prius cars before I got a house with a garage so I know how you feel. I like Tyrod's post. If they go in a bucket, you don't have to worry about the environmental impact of the rodent going in the belly of an owl for instance. Didn't think of that one. The some what good part of my story is that the ignition wire insulator material killed the rat.