Malfunctioning turn signal lights may be the result of damage beyond the light bulbs or the circuits. If you've already checked these parts and the turn signal light still behaves strangely, then you might need to divert your inspection to the turn signal switch. To verify the damage to your car's turn signal switch, you may do the following steps:
When one turn signal light doesn't work upon turning it on, then you need to check the bulb. This is to see if the bulb's filament is broken. Most probably, the filament has given up after years of service. Another way to verify turn signal switch damage is to check the ground. Due to dirty contacts, the ground may not be seated properly in the socket. If you don't find any problem with the ground, then it may be a case of corrosion in the socket itself.
If you notice that two of the turn signal lights from one side of the vehicle have stopped working, then the turn signal light bulb might be worn or damaged. Replace the bulb immediately to prevent the hazards of driving without or with incomplete turn signal lights. However, if the bulb is not the problem, check the grounding in both sockets. Repair or corroded sockets if necessary.
This usually happens when you've got a broken flasher; the turn signals don't flash but still light when you turn them on. To confirm if the problem is caused by the busted turn signal switch, examine the flasher first. Replace the flashers if you find them to be damaged beyond repair. Installing brand new flashers allows your car to have flashing turn signal lights again.
An incorrect bulb installed on the vehicle causes the turn signals to flash faster than it should. This may be one indication that the fuse needs to be replaced. If the problem still persists after replacing the fuse, then check the circuit. An open or improperly grounded circuit is another possible culprit for making the turn signals flash at irregular time intervals.