My experience is that when the IVR burns out, it takes the fuel gauge with it (a full 12 volts will fry the gauge). The temp gauge seems to be more resilient. But I have a Barracuda, where the IVR is built into the fuel gauge -- in a Valiant or Dart it's a separate component, so your result may be different.
It just occurred to me that a lot of chargers for small consumer electronics put out 5V DC -- maybe you could use one of those for bench testing.
