Flasher Relay
This component is part of Electrical Systems.
Definition
The Flasher Relay is a Relay which blinks the turn signals. It is a simple electrical circuit which works as follows:
Standard Flasher Diagram
- When the direction indicator switch is operated, a circuit exists between the battery, flasher unit and flasher lamps back to the battery. Current travels from terminal ‘B’ of the unit, through the actuating wire, ballast resistor, coil on the armature and through the flasher lamps back to the battery by way of earth.
- This current, which is insufficient, because of the ballast resistor, to light the lamps, causes the actuating wire to heat up and expand. It continues to do so until the wire stretches sufficiently to allow the main contacts to close.
- Once the main contacts are made the ballast resistor is effectively shorted out and without this resistance a heavier current flows by way of the main contacts. This heavier current passes through the armature coil and lamps which are then lit.
- At the same time, a magnetic field produced about the armature attracts the moving contact of the secondary armature and the circuit is made to the pilot warning lamp in the car. While this is happening there is, of course, no current flowing through the actuating wire and it begins to cool down.
- When it has cooled sufficiently the length and both pilot and main contacts separate. Current again flows by way of the resistor and the lamps are extinguished. This sequence continues until the turn signal is cancelled.
Bosch Flasher relay
The original flasher relay is a Bosch item (part # 0 336 150 003), in a silver, round, aluminum can (see diagram) with round prongs. It is sadly no longer available. It is mounted under the dashboard at the left hand side of the steering column, in a 4 prong connector unit.
Maintenance
If your turn signals won't come on, blink once, or blink rapidly, your Flasher Relay is likely to be the culprit.
As the original relays are no longer available (although they occasionally appear on eBay from time to time), and working indicators are a fairly essential safety feature, many people replace them with units from other suppliers.
Most modern flasher relays work electronically, no longer mechanically. The problem with modern relays is that they usually have the square tabs instead of the round prongs. They can be made to work but require soldering or ditching the original connector.
SLS in Germany (http://www.sls-hh-catalogue.de/start/index.phtml) supply a modern replacement relay with round prongs (see diagram, courtesy of them).
Replacement Flasher relay by SLS
For this relay to work, the connector needs to be rewired, as per the following diagram. An alternative would perhaps be to open up your old, failed aluminum can relay carefully, and to insert the inner workings of an electronic flasher relay kit in the old can.
Socket Rewiring
