What have I done - A side blinker story

Two approaches come to mind

1. measure voltage drops and circuit resistances on each individual leg of the running light circuit.

2. pull 1 bulb at a time until the indicator is no longer lit up. This is the method I would try first. The power that is lighting up the indicator has to be coming from somewhere and this method is interrupting circuits that might be supplying the power.

Your suspect bulbs are dash lights, taillamps, front running lamps. Does turning the dimmer switch have any effect on the turn indicator?