‘Any wiring faults other than a broken conductor need current to flow to give an indication’
Technical Consultant WE HAD A question on our Ask The Experts forum about an intermittent horn in which the reader said they had 12 volts at the horn but did not make clear if this was with the horn connected and sounding or just at the end of the cables.
The important thing to remember when using a voltmeter for test purposes is that in all but charging or battery voltage checks, any reading will be useless for diagnosis unless whatever the circuit feeds is working or trying to work.
This is because any wiring faults other than a broken conductor need current to flow before they give an indication by voltage. This is especially true with long cable runs such as a typical horn circuit. Remember that circuit fault finding using a voltmeter needs current flowing in the circuit before you will find any indication of a fault.