Jump to content

Rear Fog Light Wiring Questions


Recommended Posts

I have a 2000 Legacy GT.


There are 4 two-filament bulbs that serve as running lights/brake lights.


I wanted to know how I would run a wire out of one of these bulbs so I can hook it up to a fuse and switch so one of these bulbs can serve as a rear foglight.


I already know how to wire up the switch, fuse, and connect it to the existing front foglight wires so it is powered and works with the headlights, but I don't know what to do with the wires coming out of the rear bulb. There are 4, and I don't know whether or not to splice into one of them, disconnect one and run my own wire up to the fuse, etc.


Please help!!!


Link to comment
Share on other sites

I am not familiar with the bulb arrangment (when ON) for a 2000 Leg.


I think there is one brake/tail bulb in each of the "fender" lights, and another in each side of the trunk/hatch lights, is that right?


Do all four show bright under braking?


IF that is right, I would do one of two things, and it all depends if you want one or two rear fog lights...


I would take the inboard of the pair of bulbs on each side, and disconnect it from the high-filament braking. (disconnect both sides, to keep it symmetrical) so that just the outer two of the bulbs and CHMSL are doing the brake light duty.


Wire either just the driver's side high-filament (closest to the centerline of the road) to come on with the front fogs, or if you want to, wire both inboard high-filaments.


Some cars like the Olds Aurora have two rear fogs... But it potentially can get mistaken for riding your brakes, until you do tap the brakes, and three more bright lights come on.


Some cars, including new Legacys in non-North American markets have a single rear fog light, and it seems (probably a legal matter) that it is always on the driver's side, closer to the centerline than the shoulder of the road.

Link to comment
Share on other sites

All 4 lights light up in the arrangement.

And you are right, 2 are on the fender and 2 are on the side of the trunk hatch.


The real question now is there are 4 wires coming out of the back of the bulb.

On the right side (passenger) I don't know which wires to disconnect to disable the high filament.

However, knowing this would solve my problem for the driver side since I can just take the same set of wires (on the left though) and connect it to my switch assy.


Do you happen to know which wires control the high filament?

I can snap a picture tomorrow if that helps.

Link to comment
Share on other sites

Ok, here are some pics of what I am talking about.


The first pic is the rear of my Legacy, and the blue circle is where I want to turn the high filament into the fog lamp.


The second pic is the back of the bulb with 4 wires coming out. I know I don't want to mess with the white/stripe black since it is ground, but I don't know to disconnect the black wires or the pink one.


Does anyone else know which one I would disconnect?


Thanks everyone!!



Link to comment
Share on other sites

I am not sure which wire is the high-output filament. The White or Pink are likely positives, one for dim, one for bright. The two dark ones are probably ground.


although I am not sure why there is more than one ground, unless the brake circuit is ground-switched. you'll know that if you wire your fogs, and the bulbs still only work like the brake lights. You can check that by grounding a jumper from one or other of those dark wires directly to the chassis. If the switches are on the ground side of the circuits, that means the positive is always hot, or at least always hot with the ignition on.


Jumping from the bulb ground to the chassis ground will close the circuit and bypass the headlight switch, or the brake pressure switch, and turn one of the filaments on. Then you know it is ground switched, and your fog light switch only needs to provide that jump when closedl, which is fairly easy...


The following instructions are for a positive switched setup, if the ground jump doesn't work.


The trick is going to be this... Get your handy dandy electrical tester (light bulb type will work for this, but a meter will give you the voltage number)


Turn your headlights on, and probe each of the wires. You should get ~12 volts from one of them (while the dim filament is on.) If you have an ohm meter, you should be able to measure from the hot side to the body (ground) and get a resistance level of the dim filament, the negative side should give you less or no resistance, but you'll still see ~12 volts.


(Caution, don't test resistance with the lights on, it could spike your meter.)


Now, if one of the larger wires (pink or white) shows no positive volts, while only the dim filament is on, then it should be the high filament. If you prop the brake pedal down to get the brake lights, this should put that formerly dead wire to 12 volts. This should establish the high-filament positive lead.


There should be a color correspondence to both trunk bulbs (since they are not turn signals independent of each other, they are both probably on the same circuit.)


Now... you have two choices. You have indicated that you want the drivers side only to be the rear fog...


Do you want the passenger side trunk bulb to still work as a brake light?

Do you want the Driver's side trunk bulb to still work as a brake light when the Fog setting is turned off?


I could see going either way on either of those questions, but if you are going to leave the passenger side active for the brake lights, then leave both active, or disconnect them both from the brake light circuit. Otherwise you'll look like you have a brake bulb burned out when the rear fog is turned off.


If you have the rear fog on, there will be one bright bulb, and three dim ones. The brake lights will brighten the remaining bulbs, and turn on the brake light in the spoiler, and it will be evenly bright. If you disconnect them, the passenger side will never be bright, and the driver's side will only be bright when the rear fog is turned on, otherwise dim.


*** there is a caveat.

If the trunk bulbs are wired in series, and you splice into that wire without severing it (to leave the bulb active for the brake light circuit as well) and that bulb is not at the end of the chain, any bulbs wired AFTER it (possibly the passenger side trunk bulb, possibly the spoiler brake light, possibly-but-not-likely the brake lights in the fenders might also light with the rear fog.


If you wire it to keep the trunk brake lights, and you find that the rear fog light switch lights more than just the bulb you want, you may want to go back and either re-order the bulbs so that the brake light circuit ENDS at the bulb you want to be the fog, or clip the brake light leads for the trunk bulbs (at the bulbs, you don't want to cut out the spoiler light.) and wire your drivers side trunk bulb for Fog only.


*** I Doubt this is the case, because if they are in series, then one brake light burning out could potentially knock out several others. They are likely wired in parallel, and the below instructions should work OK.


/END CAVEAT, Continue instructions...



If you want the passenger side to be on, leave it alone. If you want it to not be a brake light any more. then clip the high filament wire, tape the hot end of the wire, and you may want to tape it to another wire to keep it from shorting to the body and blowing fuses.


If you are going to keep the brake function of the driver's side trunk bulb, then you'll want a "vampire" connector, that splices one wire to an existing circuit, without terminating the existing circuit. If you need more info, let me know. You'll simply want to sleeve the connector over the existing high-filament hot wire, and attach your lead wire from your switch, and close the connector. This will provide two sources of 12 volts to the high side of that bulb. It will be on bright when the switch is active, and when it is not active, the brake circuit will activate it, as well.


If you don't want the brake light function, then clip the high wire. tape off the hot side, and secure it, and use a barrel crimp connector to connect your rear fog lead to the bulb holder wire stub, and then the bulb will only be on high when you turn the rear fog on.


You may want to see if anybody has a BE/BH edition Legacy/Outback wiring diagram..., or if someone with one of those body-style Legacy/Outbacks wants to chime in about the wiring of the trunk brake lights...

Link to comment
Share on other sites


This topic is now archived and is closed to further replies.

  • Create New...

Important Information

Terms of Use