You do realize there can be more than one wattage of bulb fit in there right? From not enough light to too much and melt the socket. You can also get around low light by using a pencil eraser on the bulb contact are as well. Run a voltmeter over the printed strip from end to end and see if it has unusually high resistance there, that would lower power to the bulb.
You simply run down a wiring diagram and it will tell you ground and power inputs into the gauge pack. The gauges are cut down from 12 volts to 5 I'm thinking, do not apply full 12 volt to them or fry city. The bulbs are usually straight 12 volts. There is a voltage dropping resistor on the pack to lower power to the gauges so look for that and the lower amount comes after power goes through it.