Indicators not working properly
Indicator won’t work at all
Check the fuses
The simple way to this in pre-1980 MG’s is see if the wipers, tacho and fuel gauge are still working, as they all run off the same fuse.
Hazard Switch faulty
One common source of losing indicators when a hazard switch is fitted lies in the hazard switch itself. The hazard system uses a different flasher unit from the indicators, so in order not to confuse the electrics the power to the indicator switch is routed via the hazard switch so the indicators can be disconnected when the hazards are on.
The hazard switch does this by having two sets of contacts: one to operate the hazards as you would expect, the other for the indicator feed. These latter contacts are closed when the hazard switch is off, allowing current to feed through to the indicators, and open when the hazards are on thus disconnecting them. This part of the hazard switch can malfunction while the hazard part of it still works. It is a common failure.
To check for this, unplug the hazard switch and bridge across the two darker green wires in the plug – these are the power feed to the indicators and test to see if the indicators then work. If so, the only cure is a new hazard switch.
Indicator lamps work but won’t flash correctly
A second problem occurs when the indicator is flashing slowly, or the lamp comes on but doesn’t flash at all. The symptom is more pronounced when the engine is off or at idle when the charging system isn’t boosting battery voltage.
This can be down to the flasher unit needing replacement, but is most often down to a poor earth connection in the flasher lamp – usually the front one as most models have these exposed to the elements under the wheel arch. The usual cause is rust in the bulb socket (remove bulb and clean the rust out) but it could be between the lamp body and the car body.
If there is no apparent earth problem, check all the connections in the power feed to the bulb.
An unusual flash rate, either faster or slower depending on the type of flasher unit, will result from one or other of the lamps being disconnected or having a blown bulb.
Rear indicator lamp doesn’t work
Before checking the bulbs, check the connections in the boot, as luggage stored in the corners can often move and pull apart the bullet connectors.