I have only had the car for just under a year and I am not sure about that history but the electrics have been good except for recently fixing the turn indicator repeater.

If the problem started immediately after the repair, I suspect that either one of the grounds was cut, and now the grounding is taking strange alternate paths, or a power wire was jumpered incorrectly. You should ensure that the wiring for the turn signal repair is indeed going to the correct wires.

When you say local grounds--Do you mean in the boot? or whereabouts?

Yes, there's a major common ground point there, probably one under/behind the dash and probably one in the engine bay. Disconnect them and make sure there is no corrosion or oil intrusion on the terminals or on the body/frame at the connection points.