I don't know the answer to your question, but you might try looking at the hour meter itself. I would think it uses 12v dc power (I could be wrong, but it would seem strange for it to run of un-rectified power). If so, supplying it power from any switched 12 source would work. As with other instrumentation components, the hour meter ground could be your problem as easily as the supply side, so check your ground. Improper intuition seems to always cause people to concentrate on the power supply side and to overlook and assume that the ground is good. My experience leads me to believe grounding problems are just as, if not more, frequent.