Auxiliary Fog Lights for Your MINI by Roger Sitterly

Roger is making the information available to all via this post. Copied without amendment, statements and opinions are his alone.

Fundamentally, there are two reasons for adding auxiliary lights to the front of your MINI. First, you want to increase the amount of light projected down the road to improve your ability to see under specific conditions; second, you simply want the “rallye” look and you probably won’t ever light them up.

If you just want “the look”, find some lights that appeal to your sense of style, and mount them. You don’t need to worry about beam pattern, wiring, location, or legal constraints.

On the other hand, if you want to add auxiliary lights to improve your ability to see down the road, the task is somewhat more complex. Auxiliary lights tend to be classified by beam type, so the first decision to make is which of these types (or both) you need. You can buy fog lights or driving lights. They have two different names because they serve two distinctly different purposes. Beyond that basic distinction are minor differences in the actual beam pattern (for instance, at one time, Marchal and Cibié sold driving lights with oval, bowtie, and circular beam patterns, and some Cibié fog lights had an 82-degree horizontal spread while others had as much as 120 degrees of spread). In addition to beam type and specific shape, you also need to be concerned about the physical dimensions of the lights – putting a pair of Super Oscars on the front of your MINI probably won’t be possible without substantial cost simply because the lights are so large.

This article will deal only with fog lights. I’ll address the selection and use of driving lights in my next article.

Fog light design and beam pattern

As the name implies, fog lights are designed specifically to assist a driver in seeing the road after dark when there is heavy fog impeding his/her vision. They also work well when driving after dark in heavily-drifting or falling snow. Most people, when confronted with fog, simply use their low-beam headlights and let it go at that. In daytime hours, that’s generally fine because all that either fog lights or low-beam lights will do under those conditions is tell other drivers where you are. During daylight hours, that’s a far more serious concern than having additional assistance in seeing where you’re going.

Driving after dark in conditions that severely restrict forward vision is a different problem. Normal low beam headlights, even with the sharply delineated cutoff of our MINI’s low beams, can actually make it more difficult to see where you’re going in pea-soup fog or heavy blowing snow than using only a good set of properly mounted and aimed fog lights.

This problem arises because of what’s called “backscatter”. Backscatter occurs when the light from your headlights hits the small water droplets in the fog or the individual snowflakes in the air and is promptly reflected back into your eyes. The more light that’s projected into the fog or snow, the worse the problem becomes. That’s why you almost blind yourself in heavy fog or heavily blown snow if you hit high beams – you might as well be driving in white-out conditions.

Well designed fog lights mitigate (but do not completely solve) this problem. Such fog lights, when the beam is projected on your garage door, will have a high-intensity zone that is very wide but that is very skinny from top to bottom. There will be virtually no light above the horizontal cutoff, and the beam pattern will be, essentially, a very wide bar-shaped rectangle. There may, on some lights, be a little bit of light below the rectangular high-intensity area, but probably not very much.

Here are five illustrations of what a well-designed fog light beam pattern looks like
(Click on any image for a larger view)

Fog lights illustration 1
Illustration #1

This is a single fog light projected on a garage door. The light has been mounted too high off the ground for effective use as a fog light, but the beam pattern is excellent, and if properly mounted (no more than 24 inches above the road) the sharp cutoff of the beam pattern would reduce backscatter to a minimum.

Fog lights illustration 2
Illustration #2

This is from PIAA – it shows the beam design of their fog lights. Note the large horizontal spread of from 90 to 100 degrees. Also note the shape of the beam pattern itself. PIAA makes the lights available with either a clear (white) beam or an amber beam. There are competing schools of thought about the use of amber fog lights – some authorities argue that the amber tint provides better penetration in fog while simultaneously emitting less glare in the face of oncoming traffic while others argue having a full-spectrum light source provides better penetration and that no properly designed and aimed fog light will create serious glare for oncoming traffic. France used to require all fog lights be amber colored, and was one of only two or three countries world-wide to allow the use of amber-colored low-beam headlights. That has changed, and the use of amber-colored lights, whether low beam headlights or fog lights, has declined over the past decade or two.

Click here to view the PIAA Lamp Technology Guide

Fog lights illustration 3Illustration #3

This is from KC Hilites – it shows, generally, the relative areas illuminated by various types of lights. Note that fog lights usually don’t project as far ahead of the car as do low beam headlights.

Fog lights illustration 4Illustration #4

This shows my MINI’s fog lights as they illuminate the pavement on a dark night with no ambient light sources in the area. The photo was taken from right next to the driver’s side fender of the car, and there are two things to note. First, the driver’s side light is aimed higher than that on the passenger’s side – look at the trees visible in the left background. It’s too high, and I need to lower the aim of this light. Second, the beam pattern strikes the pavement so that the high-intensity portion of the beam is on the surface of the road only a few feet in front of the car. The two dark stains you see on the pavement are approximately 25 feet in front of the car.

Fog lights illustration 5Illustration #5

For comparison purposes, this shows my MINI’s HID low beam headlights taken in the same position and with the exact same camera settings as in Illustration #4. Both beams are properly aimed. Note that the trees visible on the left side of the fog light photo are not seen here but that more of the road surface on the right-hand side of the pavement is visible a greater distance from the car. In addition, note the color temperature difference between the QI fog lights and the HID low beams. Finally, note that the low beams don’t illuminate the foreground area between the car and the oil stains as well as do the fog lights. This forces your eyes to focus further down the road and provides more usable light where you need it under conditions when the use of low beam lights is appropriate.

Location and aiming

Well-designed fog lights should be mounted as low as reasonably possible so the beam pattern can get under most of the fog or snow, thus reducing the amount of backscatter. The Tire Rack suggests a height of between 10 and 24 inches above the road surface, with lower being better. Mounting fog lights above the bumper of any vehicle essentially puts them too far above the ground to be of any real value. The Society of Automotive Engineers (SAE) guideline for aiming fog lights (J583) says proper aiming technique is as follows:

  1. Park your MINI on the level so the front of the car is 25 feet from a light-colored wall.
  2. Measure the vertical distance between the center of the fog light and the ground.
  3. Place a horizontal mark on the wall at that height (I use blue painter’s masking tape).
  4. Aim the lights visually so that when the light is facing straight forward, the top of the fog beam’s high-intensity portion is four inches below the mark on the wall.

Daniel Stern Lighting has much more extensive directions, and tells you how to accommodate a variety of mounting heights, how to settle the suspension, how to determine the axis of each light, and the load simulation you should have in the car when you aim the lights.

Proper aiming will ensure that your lights provide the best possible illumination for you, and at the same time you won’t blind oncoming drivers with them. NOTE: Fog lights ARE NOT DESIGNED TO HELP YOU DRIVE FAST IN CONDITIONS OF POOR VISIBILITY. They are designed to help you see where you’re going when you can’t otherwise see well. DO NOT overdrive your fog lights – if you can’t see what’s ahead of you, you could very well hit it or go straight when the road turns.

Using fog lights

My personal experience in fog and heavy snow is that up to a certain point (determined by the amount of backscatter I get from low beams), using low beams plus fog lights provides the best possible amount of usable light on the road. Above that point, however, I turn off the low beams but leave the running lights on (so my tail lights are lit) and navigate forward with only the fog beams. At such times, it’s probably safe to go no more than about 20 mph no matter what kind of lights you have or how good they are, so I don’t worry about turning off low beams – the fog lights are bright enough that on-coming traffic can see them and know I’m out there, and the fog lights alone provide sufficient light to drive safely at such slow speeds.

Fog lights don’t help you very much, if at all, when there’s no fog or heavy snow falling, so leave them off when the weather is clear. They won’t help you see where you’re going. In fact, using fog lights in clear weather will actually hinder your ability to see well. As shown in illustration #4, fog lights provide foreground light – light that’s on the pavement very close to the front of the vehicle. As Stern has pointed out, “in clear conditions, more foreground light is not a good thing – it’s a bad thing.”

The reason more foreground light when it’s clear is a bad thing is that in clear conditions you’re probably going fast enough that you’re over-driving the distance the fog light’s beam is projected, meaning that whatever you see from that light will be past you before you can react to it. Instead, you should be focusing on things further down the road. Increasing the amount of foreground light over what is naturally provided by properly-aimed headlights and/or driving lights causes the pupils in your eyes to react to the bright, wide beam of light from the fog lights. The pupils constrict, reducing the amount of light they admit to the retinas, and this will substantially reduce your distance vision. This situation is aggravated because there’s no commensurate increase in the amount of light projected into the distance, where your eyes should be focused. As Stern notes, this is insidious and you are misled because “high levels of foreground light give the illusion, the subjective impression, of comfort and security and ‘good lighting’.” In practice, this means you’ll see the soda can that’s about 50 feet ahead of you, but you won’t notice the deer starting to come out of the ditch about 50 yards up the road.

Stay safe – use fog lights for the purpose for which they are designed and don’t expect them to do double-duty as driving lights.

Wiring fog lights

The easiest way to wire fog lights is to have them pre-installed at the factory. That way all you need to do is turn them on when needed. They’ll already be wired so they can’t be used unless the running lights are on, and if you have your headlights on, they’ll work only when you have selected low beam. If you flip to high beam, they’ll turn off, then come back on when you revert to low beam. The only thing you might want to do is check to see that they are aimed correctly.

If you add fog lights as an after-purchase option, however, you’ve got a bit more work to do. You will need a wiring diagram for the car (the Bentley manual has excellent diagrams, though finding the right one is a major task). You’ll also need common wiring tools – pliers, a wire cutter and wire stripper, and maybe some electrical tape. Zip-ties are great for bundling things together after the work is done, and they can help you keep the wires out of harms’ way by anchoring your wiring to another part of the car’s electrical harness. In addition to wire (14-gauge or heavier – and you’ll want separate colors for hot and ground circuits) you’ll need a switch, an assortment of connectors (or a soldering gun and resin-core solder if you decide to go that way), perhaps some shrink wrap, two 10-amp in-line fuses, and a 20-amp fused relay. Your lights may come with a wiring harness, and may contain a switch and a relay, which will save you some time and money. NEVER wire auxiliary lights without a relay! Once everything’s ready, proceed as follows (CAVEAT: The directions below tell you how to wire your fog lights so they can be either on or off when your low beams are on. I can’t tell you how to wire them so you can turn them on when only the running lights are on because all lights in a MINI are only indirectly controlled by the switch – the direct control is from the car’s computer.):

  1. Disconnect the battery of your car.
  2. Find a wire that feeds power to your low beam lights. You will tap into this wire.
  3. Find a location for the relay. Don’t hide it, because if the fuse blows you’ll want easy access.
  4. Find a location for the switch you’re going to use to turn the lights on or off.
  5. Run a wire from your tap into the low-beam power source found in #2 above to your switch.
  6. Run a wire from the other side of your switch to terminal #85 on the relay. CAVEAT: Check the wiring diagram that comes with or is molded into the body of your relay. I’ve used the terminal numbers from the relay I used for driving lights on my car, but I can’t guarantee the numbering scheme is consistent across all makes of relays.
  7. Run a wire from terminal 86 of the relay to a good, solid ground.
  8. Run a wire from a good power source (the hot side of a fuse block or other good power source) to terminal 30 on the relay.
  9. Run a wire from terminal 87 on the relay to each of the fog lights, placing one of the 10-amp in-line fuses into each wire before it reaches the fog light. Some relays come with two output terminals and you may be able to wire one fog light to each output terminal. Check the wiring diagram for your relay.
  10. If your lights came with separate power-in and grounding wires, connect the grounding wires to a good, solid ground. You may need to add a length of wire to reach a good ground. Some lights ground themselves on the mounting bracket, assuming that bracket makes good contact with the car’s chassis. I’ve never put much faith in that, so I’ve always run a separate grounding wire, which is what I recommend.
  11. Double check all your connections. If you put shrink wrap over each connector as you went, heat it carefully until it shrinks tightly around the connector.
  12. Reconnect the battery, start the car, turn on low beams, and turn on the fog lights. Then, flip to high beam to see if the fog lights go off as they should. Once you’ve made sure the fog lights work correctly, you can aim them. You’ll probably need to re-program your windows and re-set your car’s clock, but then you’re done.