The dimmer itself was the culprit in my truck. If you can get the dash lights to work by pulling out on the dimmer knob, then it is the rheostat inside the dimmer. You can open the dimmer switch up, but it isn't really serviceable.
There are three wires coming to the dimmer: + in, + out, and ground. You can make a splice/jumper with a short piece of wire and two male connector ends. Plug the jumper into the dash side of the harness, completing the hot circuit. If your dash lights come on, then your dimmer is bad, and you can run it without the dimmer until you can find a replacement.