jbplock
01-01-2005, 06:24
I have thought about modifying my fog lights such that the OEM fog light switch would work independent of the High/Low beam switches. Unfortunately I don’t think there is an “easy” way to do it with out adding some electronics… I’m not sure how the 01’s and 02’s work but on my 03 the pressing the Fog Light switch will momentarily apply a ground to the BCM’s Fog Light input. The BCM appears to “latch” this ground (low) input signal and the Fog lights stay on when the low beams are on – even if the highs are switched on and off… The fog light circuit (latch) resets when the truck is shut down. Here a two possibilities for a mod:
1. Wire a separate switch (and diode if the 02’s switch 12v) directly to the fog light relay. On the 03’s the BCM applies a ground to the fog light relay. This would turn on the fog lights independently of the BCM. When the switch was “off” the Fog lights would be in the OEM configuration. There are some disadvantages to this method. I’m not sure if the BCM would like to see a ground on it’s output when the fog lights are off. Most likely (on the 03’s) the BCM uses Open Drain FET (or open collector) switches, which should be able to handle the ground. If the 02 BCM switches 12v to the relay, then a diode in series with the added switch should work. Another disadvantage is that if the fog lights are on when you turn off the ignition, they will stay on until the added switch is turned off.
2. Add an external logic circuit (latch) and relay. The input to the circuit would be wired to the OEM fog light switch. The circuit would latch the momentary switch input and turn on a relay (or solid state switch) that is connected to the OEM fog light relay (the BCM output to the fog light relay would be disconnected). Power to the circuit would come from the ignition circuit such that it would reset and turn off the fog lights (if they were on) when the ignition is turned off. This would be the ideal solution but would require a little design and packaging. There may also be a ready made re-settable latching relay/switch available that could be adapted for this. This is currently on my to do list If I ever get some time to do the mod I’ll post results …
Does anyone have some other thoughts/ideas on ways to accomplish this?
smile.gif
1. Wire a separate switch (and diode if the 02’s switch 12v) directly to the fog light relay. On the 03’s the BCM applies a ground to the fog light relay. This would turn on the fog lights independently of the BCM. When the switch was “off” the Fog lights would be in the OEM configuration. There are some disadvantages to this method. I’m not sure if the BCM would like to see a ground on it’s output when the fog lights are off. Most likely (on the 03’s) the BCM uses Open Drain FET (or open collector) switches, which should be able to handle the ground. If the 02 BCM switches 12v to the relay, then a diode in series with the added switch should work. Another disadvantage is that if the fog lights are on when you turn off the ignition, they will stay on until the added switch is turned off.
2. Add an external logic circuit (latch) and relay. The input to the circuit would be wired to the OEM fog light switch. The circuit would latch the momentary switch input and turn on a relay (or solid state switch) that is connected to the OEM fog light relay (the BCM output to the fog light relay would be disconnected). Power to the circuit would come from the ignition circuit such that it would reset and turn off the fog lights (if they were on) when the ignition is turned off. This would be the ideal solution but would require a little design and packaging. There may also be a ready made re-settable latching relay/switch available that could be adapted for this. This is currently on my to do list If I ever get some time to do the mod I’ll post results …
Does anyone have some other thoughts/ideas on ways to accomplish this?
smile.gif