Those are probably the only two gauges on your dash circuit the limiter controls, and you are having trouble with both. I'm suspect of the limiter. However, when you grounded the wires, did the gauges peg to the end? If they did, the limiter is still good, and putting out five volts as it should. The sending units are actually variable grounds, eliminating them by grounding the wire lets five volts through the gauge, pushing each to max reading. If the limiter fails, gauges either won't read, or be on the low side.