1995 XJ6; right turn signal operates normally. Left turn signal flashes at twice the speed which is supposed to indicate a bad bulb. When the left turn signal is operating the bulb failure warning light illuminates. However when physically checking the light all of the left signal lights are functioning as well as all brake lights. How does the system detect a bad bulb? High resistance, voltage drop or??? How do I correct this or am I being too picky?

 

Not sure on your market.

The most common issue down here is the multi pin loom plug at each corner of the front under tray, where it meets the front guard liner.

Moisture, and gunk, gets into this plug. So locate it, seperate the 2 bits, clean the lot with Lemon juice, wash well, apply dialetric grease and replug.

Dont forget that the front indicators in the bumper have 2 bulbs each.

 

Could it also be the bulb (Just forward of the front door) on the side of the car that indicates as well?