My Disco 1 V8 1996 indicator started flashing fast like a bulb was gone. But only when indicating left. The hazard lights work ok, all bulbs are functioning. Even when indicating left, all bulbs work. I have a tow bar and socket, which has not been used in years. Could it be the flasher relay or do I start looking at more serious wiring issues?

Could be but the only way to find out is replace it.
I would also replace the bulbs u may have one with an iffy filament ie resistance is slightly lower

Thanks. I start with the relay.