T5 Horn Circuit

The T5 has a very simple 12 volt AC electrical system but one thing may not be clear when you look at the wiring diagram.

It appears that the output from the alternator goes firstly through the horn, this does not make much sense. If you are fault finding it is important that you understand how the system works.


  1. Out put from the alternator is the blue wire to the horn switch.
  2. Horn switch is normally closed.
  3. From there the yellow wire continues to the regulator.
  4. Electricity always takes the easy path, so the current passes through the switch rather than through the coil in the horn.
  5. When the horn button is pressed and the circuit is broken and then the current will have to pass through the horn and the horn will sound.
  6. Power still reaches the regulator because the horn does not use all the power available and it does not break the circuit.

Why is this unusual system used?

To ensure that all the current is available for the horn when it is operated. On any circuit the horn may not sound efficiently if it is supplied with low power.