spoon2000

I did some experimenting this morning on my '00 US spec. A6 and made some interesting discoveries in pursuit of being able to have always-on fog lamps as DRLs. FWIW I concentrated on fog lamps since the car has HID headlamps, which I don't want to run all the time, and since I didn't want to fool with trying to partially lower the voltage to the high beams (as is done on some cars) to run as DRLs.

Basically, I found that on the harness on the back of the headlamp switch, the white w/ yellow wire in position 8 is the output to the fog lamps. When that wire has 12V applied to it (via the headlamp switch being pulled out a notch or via a jumper from some other 12 volt source), the front fog lamps come on (and the multi-color "fog lamps are on" LED in the headlamp switch turns green). There is a relay involved somewhere, which you can hear clicking as power is applied or removed. The fog lamp wire pulls about 8 amps (11 or so peak) when it's powered.

When fog lamps are turned on via a 12 volt jumper to the white w/ yellow wire, nothing else seems to be affected, i.e., flashing or switching on the high beams causes the fogs to go off, and no "bulb out" indicators come on or anything like that.

I tried two sources of "on when the ignition is on" power to jumper to the white w/ yellow wire. One was the hot side of empty fuse slot 27 in the fuse compartment at the driver's door, and the other was the yellow wire going to position 1 on the back of the headlight switch.

Interestingly, applying a 12 volt power source to the white w/ yellow wire in position 2 on the back of the headlamp switch harness will cause the fog lamps to come on, even if the fog lamp fuse is removed. It seems that under the normal set-up, pulling the fog lamp fuse causes power to stop flowing to the grey w/ green wire in position 2 on the back of the headlamp switch harness. My interpretation of this is that under normal circumstances, fog lamp power comes from th fog lamp fuse to the light switch, and if the switch is set for the fog lamps to operate, the switch sends power down the white w/ yellow wire to the fog lamp relay, and then to the fog lamps. So this says to me that if a jumper was used to run the fog lamps all the time, the jumper would need to be fused at 15 amps, if not 10 amps just to be safe, otherwise the circuit would not have appropriate overload protection.

Anyway, I tried all of the above only for a few moments. I didn't smell anything burning, no fuses blew, everything was fine when I put things back to normal, etc., but I wonder if others in the brain trust could weigh in with thoughts on whether what I've outlined will work long-term or not, and if not, why not.

One thing I'd like to understand in particular is why the circuit draws 8 amps (which seems like a lot) at the headlamp switch, when the lamps themselves draw 55 watts each (110 watts total, or 9 amps) and are powered by a relay. The circuit seems to draw 8 amps even when operated normally by the headlamp switch.

Obviously, anything you try is at your own risk.

Thanks!

P.S. For those who want to mess around with this and don't know how to remove the headlamp switch, the procedure is: push the switch IN from the off position, then twist the switch to the right, then pull it toward you. The black plastic trim piece around the headlamp switch and dash light dimmer wheel can come off before or after the headlamp swtich using your fingernails or a flat-blade screwdriver.

BillVT

How does it work? Did you splice in a 10 or 15 amp fuse in the jumper? Thanks

JOECAYMAN

....any follow up post if this is a long term solution or not?

Daremo_06

With the information the original poster gave, you should be able to figure out the best way to do this with the wiring schematics. You could conceivably even wire an on/off switch to one of the blanks in the ESP location.

I haven't picked up the manual yet, but once I do, I'll look at this and see if its feasible.