Man you've got a good one! The real question is where is the problem coming from? Is it one particular area or multiple problems?
I would start with the easy basics: make sure your battery connections are secure and not corroded.
Fuse box: Fuses all good? Corrosion? Can you easily rotate each in its respective holder? Sometimes they look good but are bad at an end. Check carefully.
Next, check all the bulbs front and rear for correct ones and to make sure there isn't corrosion present. This can often create very weird things. Make sure the bulbs are the correct spec. In the trunk, the rear light clusters are easy to take out. Make sure the connector to the light housing is seated and doesn't have any corrosion. the fronts can be disconnected by their gang plug as well.
You can even disconnect lighting modules, such as the right-rear, per above, and try the lights. With one group disconnected, the flasher will flash more quickly than normal
I am taking a guess here that it could be a bad ground cluster, such as under the dash on the driver's side.
It is my understanding that the blinker is driven by one relay.
Does the car have a phone or a stereo that is non-factory? Any additional electrical devices added to the car?
Start with these and let us know.....
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