Checking switches (Audi 100 C4)

You can pierce the cable insulation with a test light with a needle contact and determine which cables are live.

Select the electrical circuit diagram that corresponds to the switch you are looking for.

First, you should check if the switches are powered; to do this, you need to turn on the ignition or lighting several times.

It is then checked whether the switch in the appropriate position conducts voltage further down the circuit.

Using the ignition switch as an example, the test looks like this:

Remove the instrument cluster to make the wires accessible.

Connect the test lamp wire to ground.

Pierce the insulation of the wire being tested with a test needle:

Both red wires at terminal 30 should be under battery voltage at all times.

The grey/yellow terminal of the P-circuit is in the "rest position" of the ignition switch under voltage, when the key is turned the power supply is cut off.

Black and yellow wire terminal X (and terminals 75) is energized only when the ignition key is in the "ignition on" position.

The thin red wire to the parking light buzzer and radio receives current when the ignition key is removed.

The black wire of terminal 15 is energized in the "ignition on" and "start" positions.

The red-black wire of terminal 50 of the engine starter is energized only in the "start" position.