Atlantic British Ltd. - Largest Independent Supplier of Parts & Accessories for Land Rovers

Fog Lamp Switch Electrical Diagrams

The fog lamp switch (as you may guess) turns the front fog lamps on and off. For both Discovery I and Discovery Series II, these genuine switches are located in the upper left area of the dash. 

Discovery I:
The Front Fog Lamp switch (AMR4138) for the Discovery I is used to energize a relay. The high current contact of this relay (K230) is what actually makes the connection to turn the fog lamps on. The contacts are fused (F8) with a 10 Amp fuse and are therefore protected against over current. Any attempt to power lamps directly with the Front Fog Lamp switch will damage the contacts because they are not rated for high current. Any auxiliary lamps should be powered with the relay. 

Discovery II:
The Front Fog Lamp switch (YUG102620G) is a "Momentary Action" switch. It only makes a connection and completes a circuit when it is depressed. The Body Control Unit computer (BCU #D162) continuously polls the state of the various switches and when it senses that one is closed, it takes the appropriate action. In this case, if the front fog lamps are off, it turns them on (conversely, if the lamps are on it turns them off). the BCU does this by energizing a relay (just like with the Discovery I). This relay is R130 and is located in the FUSE BOX - ENGINE COMPARTMENT (P108). Just like the Discovery I, the contacts of this relay are fused. The fuse is a 15 Amp fuse and is designated FUSE 3. Any auxiliary lamps should be powered with the relay. 

The diagrams below show the electrical circuit specifications and functionality you will need to know when installing a new fog lamp switch for Discovery I or Discovery Series II.