randytheking
02-28-2010, 16:54
So here’s a question for anyone that might have access to GM wiring diagrams because it’s probably going to take that level of detail to make this happen. The techs at the local dealer are either stumped or just don’t care.
My truck is a 2008 GMC Sierra 2500 SLT Four Door Diesel 4x4 and I want to control the fog lights via the fog light switch on the dash independent of the position of the headlights (high or low beam). Before anyone starts asking the “why?” question…and other than “because I want to”…I am using one of the wires that used to power the fog lights (yes, they are gone) to turn on a relay that powers something else.
I’ve seen the resistor mod and that essentially hotwires the fog lights to be on anytime the headlights are on. I’m going to reference someone else’s picture for this next part (see attachments). The top left pin of the fog light relay (where the diode jumper connects) is a switched ground that actually turns the fog lights on and off. When the fog light switch is off, it is an open ground. When the fog light switch is on, it goes straight to ground. When the high beams are on (regardless of the position of the fog light switch), it is an open ground. I need to figure out how to keep the high beams from affecting the functionality of that pin so only the fog light switch affects it.
I pulled the fuse panel on the driver’s side near the battery. It has a PCB inside it so the opening and closing of that ground may occur somewhere in there. If that’s the case, I can blow out a trace as long as it is on the outside of the PCB. I’m hoping it is a wire I can cut or a leg of a circuit I can bypass somewhere in the wiring harness or under the dash.
Any thoughts? :)
My truck is a 2008 GMC Sierra 2500 SLT Four Door Diesel 4x4 and I want to control the fog lights via the fog light switch on the dash independent of the position of the headlights (high or low beam). Before anyone starts asking the “why?” question…and other than “because I want to”…I am using one of the wires that used to power the fog lights (yes, they are gone) to turn on a relay that powers something else.
I’ve seen the resistor mod and that essentially hotwires the fog lights to be on anytime the headlights are on. I’m going to reference someone else’s picture for this next part (see attachments). The top left pin of the fog light relay (where the diode jumper connects) is a switched ground that actually turns the fog lights on and off. When the fog light switch is off, it is an open ground. When the fog light switch is on, it goes straight to ground. When the high beams are on (regardless of the position of the fog light switch), it is an open ground. I need to figure out how to keep the high beams from affecting the functionality of that pin so only the fog light switch affects it.
I pulled the fuse panel on the driver’s side near the battery. It has a PCB inside it so the opening and closing of that ground may occur somewhere in there. If that’s the case, I can blow out a trace as long as it is on the outside of the PCB. I’m hoping it is a wire I can cut or a leg of a circuit I can bypass somewhere in the wiring harness or under the dash.
Any thoughts? :)