Tired of only being able to turn the fog lights on with the low beams? The following modification I performed on my 04 Evo piggybacks the stock fog lamp system without cutting any wires and allows the fog lamps to work independently of the low beams.

This modification requires building a small simple circuit with parts availible at your local RadioShack. The circuit is then installed under the dash with 4 simple wire hookups.

Note: This circuit can be switched on and off repeatedly, however once switched off, there is a 2 second delay before you can switch it back on as the capacitors discharge.

The Circuit

Parts needed:

1 - BC337 or similar small-signal NPN
1 - IRF530 n-channel MOSFET
1 - D1 1N4001 silicon diode
1 - R1 1M 0.25W
1 - R2 4.7M 0.25W
1 - R3 10k 0.25W
1 - R4 330k 0.25W
1 - C1 220nF ceramic disc, polyester or mylar film
1 - C2 100nF ceramic disc, polyester or mylar film
2 - 12v relays
Misc Wiring
Project Box
1 - Circuit board
Once you have aquired the parts build the following circit:



Note: when wires intersect WITHOUT a dot there is no connection.

There are 4 external connections to this circuit. One connection to ground, One to the fog lamp relay's ground, one to the fog lamp switch and one to a 12v power source (parking lamps, ignition.... this is the power source that will determine when you can switch on your fogs)

Here is my completed circuit installed into a small project box





Installation

1) Find a suitable location under the dash to mount the box

2) Connect your ground to a chasis ground

3) Remove the plastic facia from in front of the speedo to access the back of the fog lamp switch

4) Tap into the top wire of the switch - this wire sees ground when the switch is depressed



5) Connect your 12v source wire to a wire that has 12v when the ignition is on. This will keep you from leaving the fog lamps on when you turn the key off. You could also connect this wire to the parking lamp power wire or the dash lights. This circuit is VERY low current and will not effect any of the existing electronics.

6) Run the wire labeled "to parking lamp relay" into the engine compartment to the fuse box on the drivers side. The relay pointed to in the picture is the fog lamp relay:



7) To turn the lights on we need to show this relay ground. The contact pointed to is the contact we want our wire connected to. As can be seen in the second picture below here I soldered my wire straight to the relay pin that rests in that contact.





8) Reinstall the relay:



9) Reassemble your dash and pat yourself on the back, its done!

You now have fog lamps that work when YOU want them to work

 

Discuss thread HERE!