The most simple way is once you push the button, the relay latches and stays activated, and you turn off power to the relay (turn the truck off) in order to unlatch it. Like this:
https://electronics.stackexchange.co...l-back-feature
Push once to turn on a relay and push again to turn off requires a more complex circuit. Here are a couple of pages with ideas if you want to build something:
https://www.the12volt.com/relays/spe...ations.asp#lsp
https://groupdiy.com/index.php?topic=66561.0
This one is interesting in that one of the circuits requires a long press to turn it off.
http://www.mosaic-industries.com/emb...e-power-switch
All the above would let you use a plain relay(s).
These guys make a specialized relay, it appears they had you in mind:
http://www.wolstentech.com/products/...chingrelay.php