What size bulb is an audi s4 headlight and fog light?

Check bulbs and fuse. If they are fine then check the switah. If OK it is wiring.

normal life of a halogen bulb is 1500 hrs-3000hrs. but many things can shorten this. on a side note you are not doing yourself a favor by using the fog lights at the same time as headlights. it draws your attention too close to the car while driving. leave them off. they are FOG lights. use them when its fog instead of normal lights to reduce the light bouncing back at you from the fog

First thing to check is the bulbs. The rear fog lights are the 2 bright red lights (a little brighter than the brake lights) next to the licence plate on the back of the car. They are turned on by pulling the light switch out 1 click when the headlights are on.

The fog lights on most vehicles sit directly underneath the headlight bulbs. The ballast and wiring work just like the headlights, so changing them takes not much time. The procedure to change the fog light is as follows:-- 1) Open the hood and reach down underneath the headlights to unplug the electrical plug from the fog light assembly. Squeeze the top of the release tab and pull the connection off the bulb's ballast. 2)Turn the fog light counterclockwise to remove it from the fog light housing. 3)Install the new fog light bulb.Then connect electrical plugs properly. 4) Test the fog lights by turning it ON. Thanks. you can rate this solution and show your appreciation.

The fog lights on most vehicles sit directly underneath the headlight bulbs. The ballast and wiring work just like the headlights, so changing them takes not much time. The procedure to change the fog light is as follows:-- 1) Open the hood and reach down underneath the headlights to unplug the electrical plug from the fog light assembly. Squeeze the top of the release tab and pull the connection off the bulb's ballast. 2)Turn the fog light counterclockwise to remove it from the fog light housing. 3)Install the new fog light bulb.Then connect electrical plugs properly. 4) Test the fog lights by turning it ON. Thanks. you can rate this solution and show your appreciation.

No there not connected, replace the brake light
1999 Chevrolet Blazer Auto Light Bulb Size Guide
Low Beam Headlight Bulb Size: 9006
High Beam Headlamp Light Bulb Size: 9005
Parking Light Bulb Size: 3157
Front Turn Signal Light Bulb Size: 3157
Rear Turn Signal Light Bulb Size: 3057
Tail Light Bulb Size: 3057
Stop Light Bulb Size: 3057
High Mount Stop Light Bulb Size: Assembly
Fog/Driving Light Bulb Size: 880 or 881
License Plate Light Bulb Size: 194
Back Up Light Bulb Size: 3156
Front Sidemarker Light Bulb Size: 194
Ash Tray Light Bulb Size: 161
Glove Box Light Bulb Size: 194
Map Light Bulb Size: 168 or 211-2
Step/Courtesy Light Bulb Size: 168 or 211-2
Trunk/Cargo Area Light Bulb Size: 211-2
Under Hood Light Bulb Size: 93
Instrument-General Light Bulb Size: 161 or 37 or PC194 or PC74
Check Engine Indicator Light Bulb Size: PC74
Hi-Beam Indicator Light Bulb Size: PC74
Seat Belt Indicator Light Bulb Size: PC194
Brake Warning Light Bulb Size: PC74
Automatic Transmission Indicator Light Bulb Size: 194
Directional Signal Indicator Light Bulb Size: PC74
As for the horn, inspect the fuse and relay and most common it would be a bad ground wire or worst a bad horn due to corrosion. Horn will be located in the drivers side fender.
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Fog/Driving Light Bulb Size: 880
Here is the rest of the bulb size used in your Montana.
2000 Pontiac Montana Auto Light Bulb Diagram
Low Beam Headlight Bulb Size: 9004
High Beam Headlamp Light Bulb Size: 9004
Parking Light Bulb Size: 4157NALL
Front Turn Signal Light Bulb Size: 4157NALL
Rear Turn Signal Light Bulb Size: 3156
Tail Light Bulb Size: 3057
Stop Light Bulb Size: 3057
High Mount Stop Light Bulb Size: Assembly
Fog/Driving Light Bulb Size: 880
License Plate Light Bulb Size: 168
Back Up Light Bulb Size: 3156
Front Sidemarker Light Bulb Size: 194
Ash Tray Light Bulb Size: 558
Glove Box Light Bulb Size: 194
Map Light Bulb Size: 168
Dome Light Bulb Size: 562
Step/Courtesy Light Bulb Size: 168
Trunk/Cargo Area Light Bulb Size: 212-2
Daytime Running Light Bulb Size: 3157NALL
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This may help
Low Beam Headlight Bulb Size: 9003/HB2
High Beam Headlamp Light Bulb Size: 9003/HB2
Parking Light Bulb Size: 3157LL
Front Turn Signal Light Bulb Size: 3157LL
Rear Turn Signal Light Bulb Size: 3157LL
Tail Light Bulb Size: 3157LL
Stop Light Bulb Size: 3157LL
High Mount Stop Light Bulb Size: 2825
Fog/Driving Light Bulb Size: 899
License Plate Light Bulb Size: 6418
Back Up Light Bulb Size: 3156LL
Front Sidemarker Light Bulb Size: 194
Map Light Bulb Size: 3886X
Dome Light Bulb Size: 6411
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I got a genuine one off eBay for a fraction of the cost.
Mike

The adjustment screws/nuts should be located either on the top of the headlamp assembly, behind the headlamp assembly, or near the frame rail by the radiator support.

You will have vertical adjustment screws for each independent beam (separate highs and separate lows, but will be same screw if highs and lows are the same bulb). You may also have additional horizontal adjustment screws as well

Park your car on a level ground 30 feet from a wall and measure the height from the ground to the bulb and mark on a wall (do this for highs beams and low beams if the bulbs are separate, if highs and lows are the same bulb, only do it for the lows)

For Low Beams: If the headlights read VOR, then aim the brightest part or cutoff part just below the mark on the wall. If it says VOL or nothing, aim them 2 inches below the mark on the wall.

For High Beams (if separate from low beams): Aim the headlight directly at the line you marked on the wall.