I found this on the NET. I have also recently seen an inexpensive kit from one of the parts houses that does Hi/Lo beam with Hi selected for $10.00. I can't remember where at the moment, but I'll keep looking.
These instructions will explain how to modify your C5’s wiring to have either the fog lights or the low beams come on SIMULTANEOUSLY with the high beams. The wiring can be done EITHER under the hood OR inside the car under the dash for either mod. There is an optional hidden switch that will allow you to easily return the light functionality to stock. If you want to be able to quickly return the lighting functions back to stock from inside the car then the ‘under the dash’ instructions are for you. If you don’t care about being able to control the on/off function of the mod from inside the car then the ‘under the hood’ instructions are definitely easier to install. It is possible to have ALL of your lights come on at the same time whenever only the high beams are supposed to be on if you were to combine both the low beam and fog light instructions. However, it would not be wise to supply both your fog lights and low beams from one source and just one fuse. If you must mod your car so all six lights are on together then please use two separate relays that are supplied from different fuses.
Under the Hood Instructions
Under the Hood mod wiring schematics
Parts: You'll need 3 in-line quick connects (the folding gizmos that tap into a wire without having to cut it), an in-line 20 Amp fuse, about 20' of wire (18 gauge should be fine), some 1/4" female spade terminals, some wire nuts, a 30 Amp automotive relay, and some electrical tape and zip-ties. You can get all of this at Radio Shack or Wal-Mart for under $20.
Connect a wire with a quick connect to ONE of the (+) wires that supplies either high beam (Dark Green w/White stripe on drivers side and Light Green w/Black stripe on passenger side), on the other end of that wire attach a 1/4" spade and plug it in to a coil pin of the relay (#86 on $5.99 Radio Shack relay 275-226). Attach another wire to the other coil pin (#85) and connect it to a ground point in the engine compartment, any screw attached to metal will work since the relay coil draws almost no current.
Run a wire from the Red (+) terminal on the outside of the engine compartment fuse box to the in-line fuse. Connect the outlet of the fuse to one of the switched connections on the relay (pin #87 on the Radio Shack relay). For the LOW BEAMS to come on with the high beams: Connect two more wires with quick connects, one to EACH of the low beam supply wires (Yellow on the drivers side and Tan w/White stripe on passenger side). Run each of those wires to the relay, but don't connect them yet. Now connect a short length of wire to the other switched connection on the relay (pin #30) and use the wire nut to connect those three wires. (note: it is possible to use just one wire from the outlet of the relay going to just one of the headlight wires, but then you will be running the current through both of your engine compartment headlight fuses in addition to the in-line fuse that you just installed in order to supply power the side that you didn’t connect to, and that’s just not a good idea)
For the FOG LIGHTS to come on with the high beams: Connect another wire with a quick connect to one of the Purple wires going to either of your fog lights. Connect the other end of that wire to the other switched connection on the relay (pin #30). Your low beams (or fog lights) will now come/stay on whenever the high beams are on. If you want to be able to quickly return the car to stock then just add an on/off toggle switch into the coil side of the relay wiring (pin #85 or 86). You’ll have to pop the hood to flip the switch and return the car to stock, but it may be necessary for those of you with inspections. Use the zip-ties to neatly secure the wiring runs in the engine compartment, and be sure to adequately cover any exposed wiring connections with electrical tape in order to prevent a possible short if your engine compartment were to get wet.
Under the Dash Board Instructions This is what you're doing:
Under the Dash Fog/Hi Beam mod wiring schematic The theory: The +12V that powers the high beams (Light Green wire) pulls in the relay. If the toggle switch is off, nothing happens and your car appears to be stock. If the toggle switch is on, when the relay is pulled in then the +12V from the Aux Power wire is connected to the fog lights (Purple wire) or the low beams (Tan wire) and the fogs/low beams are lit at the same time as the high beams. Here are the stock schematics:
Hi Beam Schematics Fog Light Schematics Aux Wires Schematics Here are the
parts you'll need Note: there are two relays in the picture, you'll only need one. I used a 30A automotive relay from Radio Shack, part #275-226 for $5.99 The optional switch that I used is part #275-648 from Radio Shack for $2.99, but it requires soldering the wires on to it. You can get a different switch that has 1/4" spade plugs and it will work just fine if you can't solder. The wire is 18 gauge, and the other pieces are butt splices, crimp-on 1/4" female spade terminals, and in-line quick connects. You’ll also need electrical tape and some zip-ties. The procedure: Disconnect your battery (-) terminal. If you don't you will probably blow a fuse or shock yourself. Under the passenger side footwell, at the top left corner there is a plug with three wires taped together. This is the Aux Power connection point, and the wires are Yellow, Orange, and Black. Run two strands of wire from the passenger footwell to the drivers side under the steering wheel. Connect one of those wires to the Black aux power connection. The other wire can be connected to either the Orange OR Yellow wire, if you use the Orange wire the fogs/lows will come on if you pull on the 'flash to pass' lever even if the car isn't running. If you use the Yellow wire the fogs/lows will only come on with the brights when the car is running. Make sure to remember which wire is which on the drivers side of the car. Pry out the fog light on/off switch and disconnect the plug from the back of the switch.
See pic The wire that you are interested in if you’re going to have the fogs come on with the high beams is the Purple one. You can do this mod without removing the bottom half of the dash cover, but it would be easier if you just remove it. See the instructions on how to install a Column Lock Bypass kit in the C5 Tech Tips section for details on the dash removal. You will need to remove the plastic cover that's directly above your feet when you're driving. The front has two 'push in' plastic retainers that just pull out, and the back has a metal washer that grabs onto a metal post. The metal washer will come off if you pull hard enough and twist it back and forth. The recessed part of that plastic piece is where I mounted the toggle switch.
See pic . I pulled the fog light switch wires out through the bottom of the dash board to make it easier to work on them. You should be able to push back the electrical tape wrapped around the wires to get at the Purple wire at the base of the dash, instead of next to the connector at the switch. Under the steering column, at the base of the dash, you'll need to locate the largest connector under there and unplug it. It has two rows of about 12 wires each. On one end there's a White wire on top of an Orange wire, and on the other end there's a Light Green wire on top of a Tan wire. The connector comes loose by pushing down on the center catch and pulling it out.
See pic Use the schematic drawing to be sure to connect everything properly. Make sure to have a plan for mounting the toggle switch before permanently attaching any wires. Tap in to the Light Green wire on the corner of the large connector using a quick connect and run that wire to the toggle switch. The other wire from the toggle switch gets connected to a coil pin on the relay (#86 on the Radio Shack relay). If you are not installing the toggle switch then just connect the Light Green wire directly to the relay. Connect the wire coming from the passenger side that is attached to the Black aux power wire to the other coil pin on the relay (#85 on the radio Shack relay). Connect the wire coming from the passenger side that is attached to the Yellow or Orange aux power wire to one of the switched pins on the relay (#87 on the Radio Shack relay). For the FOG LIGHTS to come on with the high beams: Tap in to the Purple wire on the stock fog light switch wires using a quick connect and attach the other end of that wire to the other switched pin on the relay (#30 on the radio Shack relay). For the LOW BEAMS to come on with the high beams: Tap in to the Tan wire right next to the Light Green wire on the large connector using a quick connect and attach the other end of that wire to the other switched pin on the relay (#30 on the radio Shack relay). Plug the large harness back in under the steering column, then reconnect your battery and try it out. The fog lights (or low beams) should come on whenever the brights are lit. Note: if you used the Yellow wire on the aux power connector then it will only work if you turn the ignition key to ACC or ON. The toggle switch must be on for it to work, and when it's off the lights will function just like they did before the mod was installed. If it works then put your dash back together and go for a drive on a poorly lit road as soon as the sun goes down. If it doesn't work then check fuse 7 or 11 in the passenger footwell fuse box. If the fuses are good check to be sure that the quick connect taps are squeezed together completely. A voltmeter or test light will work great to help see where the problem is. Use the zip-ties to neatly secure the wiring under the dash, and be sure to adequately cover any exposed wiring connections with electrical tape in order to prevent any possible shorts.
