I used to work for a custom van customizing place in San Diego in the mid 70's and we used thhn/thwn inside the van, console wiring,lighting thru out van etc. all from a fuse block, as for inside the engine comp. did do much there. but I do have a old 65 ford truck and the old guy I got it from was JCWhitney crazy and he did lots of stuff, using thwn and it still ok and i've had the truck for 15 years now, and some of it is in the engine compartment.
