B7 S4 HID Fogs - Before & After

I just finished installing HID/Xenon Fog Lights on my B7 Audi  S4 and it was super easy! The only tool you need is a T25 Torx bit and a pair of hands and you’re ready to go. I was worried I would have to remove the front bumper to do this, but luckily that was not the case. It took about 30 minutes to install the HID kit and is something that even a beginner DIYer should be able to tackle.

The HID kit I chose for my B7 (2005.5-2008) Audi S4 is made by XenTec and uses “slim” ballasts which makes them super easy to mount. The kit is about $40 which is pretty affordable, and you can pick a variety of colors depending on how bright you want them. I went with 6000k which is a nice, crisp white like the OEM bulbs. You can buy the kit from Amazon using the link to the right.

Below you’ll find a step-by-step guide on installing the HID kit on your B7 Audi A4 or S4.

Step 1 – Remove Fog Light Grilles

B7 Fog Light Grille Removal

Locate the two tabs along the upper-inside edge of the grille. You can see one pictured above and the next pictured below. Pull downward on the tabs to release and then gently pull the grille away from the car and it will pop out.


Once the grille has popped off you can see each tab as pictured below. Place the grille aside as you’ll reinstall it later.

B7 Fog Light Grille Removal

Step 2 – Remove the Fog Lights

B7 Fog Light Removal

Next remove the fog lights themselves by removing the three screws pictured above. They are T25 torx bits and simply unscrew like a normal screw would. Once the screws are removed the glass housing will pop out and you can then remove the halogen bulb by pressing in the tab and pulling the wiring off the back of the bulb.

B7 Fog Light Removal

Step 3 – Connect the HID ballast & bulb

HID Ballasts B7 Audi S4

Next, you can install the HID kit. The OEM factory wiring plugs into the back of the ballast, then the wiring coming out of the ballast plugs into the bulb, matching the red wires and black wires to each other, as pictured below:

HID Wiring B7 Audi S4

Next insert the bulb into the housing and turn clockwise to lock it in. Once locked in, turn the fogs on real quick to ensure all of the connections are solid before screwing the fog light housing back into place. If the fog light doesn’t light up, check your connections and wiring to make sure nothing is loose or mis-matched.

HID Wiring B7 Audi S4 Complete

Step 4 – Mount the HID Ballasts and Reinstall Everything

HID Ballasts on B7 S4 Fog Lights

The HID kit comes with double-sided tape to mount the ballasts with. Stick the tape to the plastic side of the ballast (not the metal side) and then find a place to tape up the ballasts. Make sure the metal side of the ballasts are not touching any plastic as it gets hot enough to melt plastic. I mounted the drivers side as pictured above, and the passengers side as pictured below.

HID Ballasts on B7 S4 Fog Lights

Step 5 – Admire Your HID Fogs

B7 Audi A4 and S4 Fog Lights DIYThe difference in light output & color is huge! I took a few shots to compare before and after with the drivers side having the HID kit installed, and the passenger side being the OEM halogen bulbs. It’s quite the difference, and these photos don’t even do it justice.

Here’s a side-by-side comparison of the light output:

B7 Audi A4 and S4 Fog Lights DIY

Any questions? Let me know in the comments below…

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