Tony, RE " internal horn relay " : page 97.64 Bentley book, current track 53 shows the horn, and internal stuff, but that little coil in the horn is the coil of the horn, which is not really a relay. A relay has a coil like that but what makes it a relay is the coil energizes ( pulls - it's an elctromagnet ) contacts for another circuit. thus providing what a relay does : It isolates the switching function from the load function. Withot relays the ignition switch would have to be huge to carry the starter motor current, for example. a starter solenoid is a perfect example of a relay, it jumpers the two contacts which connect battery voltage to the starter motor, it also happens to pull the starter gear into engagement at the same time, which is why a solenoid is so big for a relay. You can see in current track 53 that power is supplied by fuse S 12 to the horn on one side of the coil. when ground is supplied to the other side of the coil by the horn button the circuit is complete. the way horns and buzzers work, the contacts ( which are movable ) are normally kept closed by a spring - the coil engergizes, and it pulls the contacts apart, breaking the circuit, but the springs pull the contacts back together re-energizing the coil, which pulls the contacts apart, over and over, thus the buzzer effect, or in the case of the horn, an amplified buzzer thru the " horn " part of the horn.
you can see in the little drawing that the contacts are normally closed. they don't show you that the coil pulls them into non-contact, but that's how it works. scott |
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