Disconnection detection device

1. A disconnection detection device for an in-vehicle device having a load circuit, a load drive circuit which controls supply of drive power for driving the load circuit, and a first wire harness which has one end connected to the load drive circuit and the other end connected to the load circuit and supplies the drive power from the load drive circuit to the load circuit,

wherein the disconnection detection device detects disconnection of the first wire harness,

the disconnection detection device comprising:

a second wire harness which is arranged along at least a part of the first wire harness;

a current circuit which supplies a current for disconnection detection to the second wire harness; and

a disconnection determination circuit which monitors an output voltage of the current circuit so as to determine presence or absence of disconnection of the second wire harness,

wherein disconnection of the second wire harness is detected as the disconnection of the first wire harness based on disconnection determination of the disconnection determination circuit,

wherein the load circuit includes at least two horns which output horn sound,

wherein the load drive circuit includes a drive switch which supplies the drive power to the two horns,

wherein the disconnection determination circuit monitors the output voltage of the current circuit so as to determine the presence or absence of disconnection of the second wire harness, and turns on the drive switch so as to allow the drive power to be supplied to the first wire harness in a case where disconnection of the second wire harness is detected, and

wherein the drive power is supplied to the horn connected to the first wire harness on a non-disconnection side of at least the two horns to output horn sound from the horn.

2. The disconnection detection device according to claim 1 , wherein the first wire harness is branched at a branch point and connected to each of the two horns,

wherein the two horns are connected in parallel to the drive switch, and

wherein the second wire harness is arranged along the first wire harness from the drive switch side farther than the branch, passes through the branch point, reaches one horn of the two horns, is folded without being connected to the one horn, is arranged to the branch point, and is arranged so as to reach the other horn of the two horns.

3. The disconnection detection device according to claim 2 , wherein the second wire harness includes one wire harness which has one end connected to the current circuit and the disconnection determination circuit, and the other end reaching the other horn through the one horn.

4. The disconnection detection device according to claim 2 , wherein the other end of the second wire harness is connected to the first wire harness at a connection position of the other horn and the first wire harness, or connected to the ground in the vicinity of the other horn, and

wherein a reference voltage for the disconnection determination circuit to determine disconnection of the second wire harness is set to a voltage level between a power supply voltage of the current circuit and the voltage of the ground.

5. The disconnection detection device according to claim 1 , wherein the drive switch includes a horn switch and a relay,

wherein the horn switch is turned on/off corresponding to an operation of a horn button, and

wherein in the relay, one side of a contact circuit is connected to a power supply, the other side of the contact circuit is connected to the first wire harness, and the contact circuit is turned on/off corresponding to the on/off state of the horn switch.

6. The disconnection detection device according to claim 1 , further includes a supply control circuit which alternately performs the supply and stop of the current for disconnection detection supplied from the current circuit.