I'm new to Honda vehicles and this forum, so bear with me. This is in regard to my new 26 Ridgeline. That forum is limited in real technical knowledge, from what I see. So I came here. If this is the wrong area, or not pertinent, please advise. I'm an old DIY'er so I like working on my vehicles. I know Honda can be very controlling so I'll see what my options are. I am on a quest to understand how Honda wires the headlight system via the fuse box and relays and how the computer controls these circuits. The objective is to determine the possibility of running a jumper wire with a diode from the high beam circuit over to the fog light relay to trigger the fogs via the high beams. I drive in rural northern Michigan deer country, and I want the wide light they provide to help see these things as they come out of the woods to cross the highway. I have done this on another vehicle and it works just fine. I can easily do this by adding external wire harnesses, but it would be far easier to trick the system using some jumpers and a diode in the engine bay fuse/relay box. Any techs or DIY'er with electrical knowledge interested in chiming in?

 

The lighting circuits includes a MICU (Multiplex Integrated Control Unit); essentially a BCM (Body Control Module). The MICU is part of the Under dash Fuse/Relay box.

When the high beam headlights are turned on, a ground signal is sent through the combination light switch to the MICU. The MICU has IPDs (Intelligent Power Devices - a semiconductor power switch) which allow power to go to the headlight High bulbs.

Each respective light (Hi, Lo, Fog) will already have ground at all time from other grounding points.

When the low beam headlights are turned on, a ground signal is sent through the combination light switch to the MICU. The MICU will send ground to the headlight relay (located in the under-hood fuse/relay box); with this ground from the MICU and battery power at the relay coil to energize the coil, the relay contacts will close and allow power to the low beams.

There is also an Automatic Lighting Control unit sensor that can send a ground signal to the MICU; so, that the MICU send ground to the headlight relay coil to close the relay contacts to allow power to the low beam headlights.

When the fog light switch is turned on, a ground signal is sent through the combination light switch to the MICU. The MICU will send ground to the front fog light relay (located in the under-hood fuse/relay box); with this ground from the MICU and battery power at the relay coil to energize the coil, the relay contacts will close and allow power to the fog lights.