Cannot get ASP.NET Web API routing to work at all

Question

I am trying to refactor an old setup, the end goal will be that I will have a functional REST API. I am getting rid of an old NuGet service and I sort of have to rebuild everything now. I am trying to set it up using ASP.NET Web API. This will include 60+ routes (like "www.website.com/cars/{id}/engine" "www.website.com/inventory/{id}" etc..)

I have tried attribute routing and conventional routing, and nothing seems to work. I get 404's no matter what I seem to try. I am probably just not doing either of them correctly.

Here is how I am setting up configuration (I am using a self hosting package btw but this is the main configuration point):

public class SomeHostClass
{

public void Configuration(IAppBuilder app)
 { 
  HttpConfiguration config = new HttpConfiguration();

  //If I am trying attribute based routing, uncomment this
  //config.MapHttpAttributeRoutes();

  Register(config.Routes);

  // I think I need this at all times?
  app.UseWebApi(config);
 }

public void Register(HttpRouteCollection routes)
 {
    // One of many other routes.MapHttpRoute() calls
    routes.MapHttpRoute(
    name: "Cars",
    routeTemplate: "cars/{id}/engine",
    defaults: new
    {
      controller = "CarController",
      action = "Get"
    },
    constraints: null);
 }

}

Then here is my Car Controller:

public class CarController : ApiController
{
    [HttpGet]
    public object Get([FromUri] CarDTO carObject)
    {
        // Some code calling a private worker method
        return WorkerMethod();
    }

    private object WorkerMethod()
    {
        // Worker method do stuff, return
    }
}

This Get() method is never called and a 404 is returned.

Another note: I have tried using reflection to register all the routes, which slims down the code. I'll debug it and it looks like all the routes have been configured correctly within the HttpConfiguration.routes but I will get 404's still. Even without reflection doing it the way shown above- if I debug and look at the values they all seem correct, but don't work.

Another Note: I should also mention that this is the error I usually get along with the 404.

{"Message":"No HTTP resource was found that matches the request URI 'http://localhost:8000/cars/1/engine'.","MessageDetail":"No type was found that matches the controller named 'CarController'."}

How do I get these routes recognized and stop returning 404's and start returning my data?

If this is a bad way of going about this- what's the best way?