Well there ya go then. Oil temp is a great gauge to use. However, without a special adapter that goes between your oil filter and the housing (cant be used on the GP 3800 due to the proximity of the oil filter to the suspension such as the lower control arm) or taping into an oil feed of some kind in the block perhaps, they are hard to set up.
unless you got a system a volt gauge is pretty useless. its only good for diagnosing when your alternator is going out. save your money and buy that one later or something if you really want it.