find were to plug in wiring harness

greetings my name is michael. I just purchased a 2006 toyota Prerunner crew cab v6 auto i am attempting to install a plug in the right rear part of the bed most come with it standard mine didnt. here is my question. I bought the wiring harness from the dealer,as well as the plug.the deal told me the wiring harness plugs underneath the pass seat. I found the plug no problem. here is were the problem is the dealer also to me that the other end plugs in on the passenger side of the engine compartment near the yellow wire that is the airbag sensor. for the life of me i cant see were it plugs in i am frustrated can anybody help me.2nd question is i bought the 100 amp fuse but i cant figure out how to remove the area that the fuse plugs into without breaking it how do i get to the area to bolt the fuse into place. pictures would be appreciated