The basic circuit Fitting the Lamp Return to Front Page
The Upgraded Circuit
Philosophy
A fog lamp that doesn't work is worse than useless. The rider goes on his way safe in the knowledge that he is well lit up when, in fact, he is nearly invisible.
What is needed is a positive indication that the bulb is working. This is relatively easy to achieve. Perhaps the simplest way would be to arrange a separate bulb failure indicator. (I have already done this for tail lamp and brake lamp) but I decided that this would be one lamp too many . Next thoughts were to use the lamp in the switch. A simple circuit would prevent the lamp from lighting unless the bulb were lit. This is OK as far as it goes but it would be only too easy to fail to notice when the warning light is lit. The best solution is to use the switch light to provide a positive indication as follows:-
Fog Lamp off - No indication.
Fog Lamp on - Steady light from switch light.
Fog Lamp not working - Switch light flashes.
Below is a general wiring diagram to show how the circuit is wired up. Click on the Circuit Diagram to show the internal circuit.