These trucks don't typically come with seat switches unless it was ordered with a neutral lock option from the factory. Those have a box mounted on the RH overhead guard, the harness for that runs through the OHG leg down to underneath the dash connects to the main dash harness there and there is also a neutral lock module mounted on the LH side under the dash. These components do connect to the main harness at some point and run back to the seat, i'm not 100% sure on the rest of it.
I've only dealt with these trucks where that option was already installed. If you want to convert a non-neutral start option truck into one you'll have to contact your cat dealer and get them to give you all the parts needed to convert the truck to that. Sometimes they have a kit, sometimes they do not and you have to buy each component individually. I looked in the 'options' section of the parts book and it does not show up as an option kit there. Unfortunately cat is like that in some cases, the only way to know for sure is to call them.