The problem with your dash is most probably due to the voltage regulator for your guages overheating and going open circuit. These regs are simple bi-metal circuit breaker types and prone to shutting down when input voltage gets too high. (High engine revs and small alt pulley). Good solution is a solid state adjustable voltage regulator kit from Jaycar or Dick Smiths, using an upgraded transistor and heatsink. If you're pulling the dash anyway, you may as well fix the problem for good.