Various early (1966 to 1969) USA delivered VW buses and bugs have a mysterious turn signal relay unit which confuses most people trying to figure it out. On the typical VW wiring diagram, it looks like this:

Here's what's functionally inside it:

[Click on the drawing to view a bigger version]

As you can see, the module contains two major subsections: a flasher unit, and a 4-way flasher relay. We will deal with each of these subsections separately.

Each subsection of this module may be tested on the bench. You will need the following:

For all tests, the '-' battery terminal will be connected to the case or center mounting screw of the 9 pin flasher module, and to the shells of the turn signal lamps.

Flasher Unit

The flasher subsection is an electronic version of a standard three or four pin flasher, and works similiarly. You supply it power, and connect a lamp load to its output. The lamp load makes the flasher relay open and close periodically, causing the connected lamps to flash. There is a third connection to the flasher unit which causes the dash indicator to flash.

The flasher unit may be tested by connecting to the flasher module as follows:

If the flasher unit is good, the two lamps will flash. If you wire a small indicator bulb between terminal 15 and terminal KBL, it should also flash.

4-Way Flash Relay

The 4-way flasher relay reconfigures the normal turn signal wiring so that all four turn signal lamps flash at once, regardless of whether the ignition key is on or off. The position of the turn signal switch is ignored, as is input from the brake switch.

When the 4-way flasher switch is pulled, it grounds terminal S on the module. This causes battery power from terminal 30 to pass through the relay coil, activating the relay. This causes the following circuit changes:

The relay coil can be tested by connecting '+' battery to terminal 30 and '-' battery to terminal S. The relay should click.

The basic switching function may be tested by connecting as follows:

The final circuit to check is the brake light switch pass-through: Test as follows:

Final Thoughts

Once you know what's inside the 9 pin flasher, and you know how it works, much of the mystery of this device disappears. Examine the schematic to understand what's inside. Follow the tests above, and conquer your 9 pin flasher.