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The fact that you can make the lights come on properly by actuating the dimmer switch indicates that the failure is likely in the dombination switch in the steering columd (which includes the dimmer switch). It is an assembly which includes the dimmer, 4 way, and turn signal switches (and possibly teh wiper switch, if that is on the turn signal lever on your car, I don't recall)...
It is a pretty easy switch to change, you don't even have to pull the steering wheel, only the shrouds on the column. If you do attempt it yourself, be sure to disconnect the battery for about 10 minutres before proceeding, as there is airbag wiring in the column also.