You have an ammeter then and you won't use the idiot light wires for it. You'll need to splice it into the large wire running between the regulator and the battery post on the starter. This is assuming there is no terminal block on the truck.
For the oil pressure you need to see if it is a mechanical gauge or electric gauge. Either way you can't use the sending unit for the light. You say it looks like you need a tube. If it's a threaded fitting with a small hole in it, it does. Your local auto parts place or hardware store can fix you up with the tubing and fittings for it.
