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Flasher Relay

This component is part of Electrical Systems.

Definition

The Flasher Relay is a thermomagnetic controller that blinks the turn signals. It is a simple electrical circuit which works as follows:


Under resting conditions the “heating wire” is cold keeping the “flashing contacts” together in the normally closed position. After turning the turnsignal switch on battery current flows immediately to either the left or right control light and the turnsignal light (49 -> 49a) . At the same time an electromagnetic field develops around the coil that attracts the “control contact” and allowing current flow from 49 -> 31 The temperature of the heating wire rises causing the wire to pull away from the flashing contact and interrupting current flow to the turnsignal lights which also diminishes the electromagnetic field. The control contact returns to its normally open position, the heating wire cools of and closes the flashing contacts again. Provided the turnsignal switch is still closed the process repeats again at a repetition rate that is determined by the heating and cooling rates of the heating wire. These flashing rates are usually about 1.5 +/- 0.3 Hz.

When metal fatigue sets in the heating wire no longer retracts or expands correctly and the flashing rate slows down or stops completely. No easy repairs are known and since these units are no longer available from the manufacturer it is best to replace the flasher unit with a modern electronic one as described below.

Mercedes used three suppliers for these units:

  • Bosch – Mercedes p/n 000 544 61 32 [Bosch p/n 0 336 150 003]
  • Hella – Mercedes p/n 000 544 83 32
  • SWF – Mercedes p/n 000 544 53 32

Bosch controller

SWF_controller

Maintenance

If your turn signals won't come on, blink once, or blink rapidly, your Flasher Relay is likely to be the culprit.

The flasher controller is located under the left (driver) side of dashboard (on LHD cars) next to the handshake connectors linking the multifunction switch wires and those from the center cluster to the main harness.

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.

A modern replacement relay with round prongs is a Kaehler 3.101.200 available from AutohausAZ (http://www.autohausaz.com/pn/0008211063).


Replacement Flasher relay

For this relay to work, the connector needs to be rewired by removing the cap and moving the black/white/green wire as shown in the photos:.


Socket Rewiring

A somewhat less expensive flasher is made by Wehrle, another OEM supplier to Mercedes:

An alternative is to open up your old, failed aluminum can relay carefully, and insert the inner workings of an electronic flasher relay kit in the old can. Note however, that only the SWF can is wide enough to insert the complete modern unit.

The old-style Bosch flashers and the newer electronic flashers shown above require a certain amount of resistance and thus cannot be used with LED bulbs in the turnsignal lamps.

Electronic LED Flasher Relays have no minimum load-12VDC. They eliminate the need for load resistors, turn signals will flash at normal rate with or without LED bulbs. That is, they can also be used with regular incandescent bulbs or a mix of incandescent and LED bulbs.

There are several versions available, usually designed for either European (CF13GL-02), Japanese or American cars. For Pagodas it is best to buy a "European version" because the pins are marked similar to the Kaehler or Wehrle electronic relays pictured above.



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