They must have put a relay in line with the ignition system, as you have found out it's not the best idea as it adds more wire length into the hole thing and this causes the ignition system to pick up noise and do odd things when the left turn signal is on. I would look at the left turn signal wiring and try to find where it ties into the ignition system. I think they may have put it under the DS wing or by the fuse box, but those are just guesses.
Don't forget to
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first then ask questions later! The loose nut behind the wheel