Just a WAG here since I am not familiar with your coach, but if it were my situation, I would start looking for a bad ground connection on the left side signals.....assuming that all bulbs use a common ground. It would be very unusual to have many bulbs fail at the same time normally. On the right side it is strange that the brake light also does not work since the grounding there seems OK (since the signals work there).....if they are two filament bulbs maybe it is just a normal burnt out bulb on the right side brake?
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