The clock and tach use 12v, The limiter takes that 12v and opens and closes a set of points very quickly to give the gas, oil, and temp guages 5v so they don't peg the needle. I think standard calls it a guage voltage limiter. Measure that regulator with a test light. You should have a light at the main wire in and a dim light at the output to the three guages. Also look on Google for the solid state one that you build using a 5v regulator and resistors from Radio Shack, that fits inside the stock piece.
Rob