Lamp failure warning circuits for road vehicles

Claim 2

A lamp failure warning circuit for a road vehicle, comprising in combination a battery having a live terminal and an earth terminal, first and second relay coils each having one end connected through the vehicle lighting switch to the live battery terminal, the other end of the first coil being connected to earth through the side lamps of the vehicle in parallel, and the other end of the second coil being connected to earth through the tail lamps of the vehicle in parallel, first and second parallel connected and normally closed contacts which are opened by the first and second coils respectively when both side lamps and both tail lamps respectively are illuminated, both the first and second contacts serving when closed to complete a circuit by way of the lighting switch and a diode to a warning lamp, a third relay coil connected to the live battery terminal through the brake lamp switch and the ignition switch of the vehicle in series, the other end of the third coil being connected to earth through the brake lamps of the vehicle in parallel, and the third relay coil serving when energized to close a third contact to complete a circuit by way of the ignition switch, the brake lamp switch, the third contact and a second diode to the warning lamp, the first and second diodes isolating the circuits from one another, and the arrangement being such that the warning lamp is illuminated whenever a side or tail lamp fails with the lighting switch closed, or whenever the brake lamps are operated with the ignition switch closed, provided neither brake lamp has failed.

Claim 3

A circuit as claimed in claim 1, including a fourth relay coil having one end connected to the live battery terminal through the ignition switch of a vehicle, and its other end connected to earth through a switch which is closed when the handbrake of the vehicle is applied, the fourth relay coil serving when energized to close a fourth contact to complete a circuit through the ignition switch to the warning lamp.

Claim 4

A circuit as claimed in claim 2 including an additional switch in parallel with the handbrake switch, the additional switch being closed when the brake fluid level falls below a predetermined value.

Claim 5

A lamp failure warning system for a road vehicle, comprising in combination a battery having a live terminal and an earthed terminal, a first relay coil having one end connected to the live battery terminal through the lighting switch of the vehicle and its other end connected to earth through the offside side and tail lamps in parallel, the first coil being energized only when both the offside side and tail lamps are illuminated, and serving when energized to open a contact which when closed completes a circuit by way of the lighting switch and a diode to a warning lamp, first and second ganged switches together constituting a parking light switch, the second switch serving when closed to complete a circuit by way of the lighting switch to one end of a second relay coil, the other end of which is connected to earth through the near-side side and tail lamps of the vehicle, the second relay coil being energized only when both near-side side and tail lamps are illuminated, and serving when closed to open a contact which in its closed condition completes a circuit bY way of the lighting switch and the first switch through the diode to the warning lamp, and a third relay coil one end of which is connected to the live battery terminal through the brake lamp switch and the ignition switch of a vehicle in series and the other end of which is earthed through the brake lamps of the vehicle in parallel, the third relay coil being energized only when both brake lamps of the vehicle are illuminated and when energized serving to close a normally open contact which when closed completes a circuit by way of the ignition and brake light switches and a second diode to the warning lamp, the diodes isolating the warning lamp circuits from one another, the arrangement being such that the warning lamp is illuminated when an offside lamp or a near-side lamp fails provided that the first and second switches are closed, but is only illuminated when an offside lamp fails if the first and second switches are opened, the warning lamp in addition being illuminated each time the brake lamps are illuminated provided that both brake lamps are operating satisfactorily.

Claim 6

A lamp failure warning system for a road vehicle, comprising in combination a battery having a live terminal and an earthed terminal, a first relay coil having one end connected to the live battery terminal through the lighting switch of the vehicle and its other end connected to earth through the offside side and tail lamps in parallel, the first coil being energized only when both the offside side and tail lamps are illuminated, and serving when energized to open a contact which when closed completes a circuit by way of the lighting switch and a diode to a warning lamp, first and second ganged switches together constituting a parking light switch, the second switch serving when closed to complete a circuit by way of the lighting switch to one end of a second relay coil, the other end of which is connected to earth through the near-side side and tail lamps of the vehicle, the second relay coil being energized only when both near-side side and tail lamps are illuminated, and serving when closed to open a contact which in its closed condition completes a circuit bY way of the lighting switch and the first switch through the diode to the warning lamp, and a third relay coil one end of which is connected to the live battery terminal through the brake lamp switch and the ignition switch of a vehicle in series and the other end of which is earthed through the brake lamps of the vehicle in parallel, the third relay coil being energized only when both brake lamps of the vehicle are illuminated and when energized serving to close a normally open contact which when closed completes a circuit by way of the ignition and brake light switches and a second diode to the warning lamp, the diodes isolating the warning lamp circuits from one another, the arrangement being such that the warning lamp is illuminated when an offside lamp or a near-side lamp fails provided that the first and second switches are closed, but is only illuminated when an offside lamp fails if the first and second switches are opened, the warning lamp in addition being illuminated each time the brake lamps are illuminated provided that both brake lamps are operating satisfactorily.