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Fog Lamp Upgrades for the Mazda MX-5 (Miata)


After I bought the car, I noticed that the fog lamps didn’t have any effect on the lighting pattern. Now, before I go any further, I believe most people have unrealistic expectations of their fog lights. Most people I’ve talked to assume they can be used as supplemental low beam lights. Daniel Stern has an excellent paper regarding fog lamps that I refer people to all the time: What Good are Fog Lamps, Really?

This led me to find one of the fog lamp bulbs was out. Well, I really prefer amber, or selective yellow, fog lamps so I set out to find amber bulbs. The stock light is an H11, so I found this on Amazon and bought it:

When I went to install them, I was surprised to find that the previous owner had installed High Intensity Discharge (HID) bulbs. Back to the drawing board – or Amazon in this case, and I ordered this:

Installing these I discovered that it wasn’t the bulb that was out, but the ballast. So I replaced the ballast along with the bulbs. Tada! Working amber fog lamps.

For a while.

The fog lamps work in conjunction with the low beam headlamps. If you read the article on fog lamps I referenced above, you’ll note that Mr. Stern advises:

The fog lamps’ job is to show you the edges of the road, the lane markings, and the immediate foreground. When used in combination with the headlamps, good fog lamps weight the overall beam pattern towards the foreground so that even though there may be a relatively high level of upward stray light from the headlamps causing glareback from the fog or falling rain or snow, there will be more foreground light than usual without a corresponding increase in upward stray light, giving back some of the vision you lose to precipitation.

When used without headlamps in conditions of extremely poor visibility due to snow, fog or heavy rain, good fog lamps light the foreground and the road edges only, so you can see your way safely at reduced speeds.

So there is some benefit from allowing the fog lamps to work independently of the low beam headlamps. There are a few conversations (threads) on the forum about making the fog lamps independent. The best option, I thought, was to have them remain switched as normal (on the turn signal stalk), but tied to the ignition rather than the head lamp circuit. The instructions are summarized here.

I like  this, as I can also use the fog lamps as Daytime Running Lights (DRLs), as many cars built recently do today. I do this during dusk to help my conspicuity (the quality or state of being conspicuous). In the bright Florida sun, I find them an annoyance from other drivers, and similarly at night when (low beam) headlights should be used. To those who say this is illegal, I refer you to Florida Statute 316.233(2):

Lighted fog lamps meeting the above requirements may be used with lower headlamp beams as specified in s. 316.237(1)(b).

(Emphasis added) May does not imply that they are required to be used with low beams. It’s permissive but not mandatory. This means they can be used without the low beams, as I’ve wired them.  If you are considering this and your car is registered outside of Florida, I strongly suggest researching the vehicle code for your state.

So here’s the rub: I rarely use my fog lamps. So I have probably less than a handfull of times I have had them on since I installed the new HID bulbs and ballasts. When I go to check my wiring, I have a fog lamp out! Double checking everything, I learn that I have a ballast out. Worse, I tried contacting the seller through Amazon, and received no reply to my inquiry about a warranty replacement. With the relatively high rating and plenty of reviews, and the choice of the previous owner for Xentec’s HID kit, I was pretty confident about this, but after doing a lot more research, Xentec just slaps their label on whatever Chinese made ballasts it can find. Finding a reliable ballast is key to an HID conversion.

An AC (alternating current) ballast is more desireable  than a DC (direct current) ballast, such as the ones Xentec uses. Even among the AC ballasts available, some are better than others, with older designs showing better reliability than new (not surprising). There are many Youtube videos to learn from. This appears to be the closest match to what’s recommended:

We’ll see how it works.

One Trackback/Pingback

  1. Arved Grass › Horn upgrade for the MX-5 (Miata) on Wednesday, February 3, 2016 at 21:39

    […] IGN (ignition on) source is the same I used for my Fog Lamp Upgrades for the Mazda MX-5 (Miata).  The instructions are summarized here. The actual connection is shown […]

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