Turn signal issue

I have 2012 Prius that developed weird issue with turn signal. Every time turn signal is activated both front turn signals flashes and both rear turn signals flashes but one is very dimmed so I haven't noticed it is on until I pulled the bulb out.
So far, I took it to dealership and they replaced headlight switch which resulted in no change in condition. They also pin check wiring from switches to control modules, ohm tested ok. Since I am out of warranty they don't want to do anything unless I agree with extended diagnostics of 10+ hours of labor.

At this point I am looking for suggestions. Any ideas what can be? I am going to get some equipment (multimeter, scope) and do some voltage measurement to try to figure out what is going on. I don't know where the flasher and relays are located on Prius. Also if someone have schematic of the circuit it would help me with troubleshooting.

 

The car was in rear accident last year around this time. The bumper and tail lights were replaced. Can it be side affect after a year? The dealer checked all ground connections in the rear and didn't see any issues.

 

I don't see any corrosion on the connectors. I found wiring diagram for 2010 Prius for Turn Signal and Hazard Lights which is hopefully similar to 2012. Looking at the diagram I would like to verify ground points A3, R2, S2. Does anyone knows where are they located in body? There also might be some kind of short between Green(Right Hand) and Yellow (Left Hand) connections which makes me think that CA1 and LR1 connectors might be suspect. There is also ground splice point for Front Turn signal that I would need to check. It seems that I have some splicing going on for the rear lights that are not indicated on the diagram.