Good luck with this, that apparent indicator bulb really does seem to be causing all the problem.
Maybe ask for the witness to be assessed on his/her eye sight, if it could be proved that they do not have the correct level of vision for drivng etc then maybe the statement about the bulb flashing, angle of sun with your approach (Work it out from time of day, car direction, and witness location obviously ) could help you out ???
Maybe ask for the witness to be assessed on his/her eye sight, if it could be proved that they do not have the correct level of vision for drivng etc then maybe the statement about the bulb flashing, angle of sun with your approach (Work it out from time of day, car direction, and witness location obviously ) could help you out ???