The column stalk connects the output of the flasher relay to the correct lights.
As it works on the right, this suggests the flasher unit is ok as well the supply to it, and the feed to the stalk.
It points to the stalk itself being at fault. To check this, remove the column shroud, and find the connector for the stalk. Disconnect the stalk, and check the plug and socket for pushed out terminals.
Turn on the ignition, and on the harness side connector (plug), get a short piece of wire and connect the light green with brown stripe wire (pin 3) to the green with red stripe wire (pin 4).
You should get left hand indicators. If so, then the stalk is faulty, perhaps a loose or bent contact in the switch.
If not, this suggests the wiring from the stalk to the header which splits out to all the indicators is broken.
Try the test above and let us know
1988 90 Td5 NAS soft top
