Add to Jeff's list:
With the ignition switch off, unplug the bulb leads and run a jumper from a hot spot on the fuse panel to the bulb feed leads. If the bulb is brighter, your dimmer circuit is the problem. If not, it's the ground, or you got the maximum voltage available to light the bulbs.
A solution is to unplug the triple connector blue-red wire for the Rally-Pac lights from the blue-red wire triple connector behind the instrument panel and plug it into the black-red triple that feeds the radio and back-up lights. It is fused and switched so your Rally Pac lights should be brighter but cannot be dimmed.
Jim