Anti-rat electrical tape? Honda has an OEM part for that.

I have been using this for years at the dealership, I promise the mice and rats will eat this also. 

I had somebody tell me to put diatomaceous earth in spots they (pack rats) might nest, as when they urinate to mark space it produces an odor they don't like. 

It seemed to work, they'd gotten up in there a couple times in a week (strut towers of the e21), and after that, no issues. 

Could be dumb luck,  I suppose, but recollection is it seemed to work. 

I don't think I've had a problem since I put the garden light on that corner of the house, but that was well after the D. E.

We had a pickup truck we kept at a deer camp.  The only thing that stopped the rodents from chewing the wires was to disconnect the battery.  For whatever reason they stopped doing it.

BIL just paid over $3K to replace a bunch of engine harnesses in his 2500 diesel PU.

A shop near me puts paper towels soaked in peppermint oil in ziplock bags spread all around engine compartments in cars in their yard.  Never a problem.  I friend does it in his RV and BMW M2.  Seems to work.  But has to be refreshed every 2 to 3 weeks.

In reply to jharry3 :

I've noticed that ants like to gather around underground electrical lines,pool lights, etc. Last time I had an electrician here I asked him if he had noticed that and if so why. He said the ants were attracted to the heat the lines and such emitted. If that's so, there may be some relationship to your battery connected vs. disconnected experience.