Both rear lights are supplied from the same wire - left hand side is fed from the right hand side wire. So if right bulb is out, but left is working, it is unlikely to be the wire. Probably just needs a new bulb.
Flashing headlight instead of turn signal ? That sounds like a wiring issue. Either wires frayed and are contacting each other or the indicator light trying to find a return to earth through the headlight bulb - which would suggest a broken earth wire at the indicator - if the headlight flashes dimly. But check the bulbs first as a broken filament can produce some weird behaviour. Then check earths for the same reason, then go hunting for frayed / broken / burnt or exposed cable.