PaulW

Last night my headlights stopped working, actually didn't turn on, this was all started by the A/C going south for about five minutes (stopped blowing cool air, had to reset the ignition to fix it) and then I figured out the following didn't work:

Headlights including high beams but "flash to pass" worked

One touch up on windows, but one touch down worked and windows went up while holding the switch

Fog lights, front and rear

Radio controls only on steering wheel

Rear defogger, rear headrest down switch on dash

Turn signals

????

So I figure it's a relay that supplies power to this stuff, not that hard to figure out, huh? However, the Bently is so damn hard to find anything on that CD, can't find electrical troubleshooting procedures, every time I look at those wiring diagrams, can't make heads or tails of them, and I've been reading schematics for over 15 years, ran nuclear power plant electrical systems on submarines for 6 years and am a electrical troubleshooting wiz. I just don't get their wire traces.......

I'm thinking it could be the load reduction relay, the one that turns the lights and other stuff off when you start the car, but I can't find on the CD where the physical location in the car is. I'd like to do that before I go easter egg hunting.

The printed manual is so much nicer, but much bigger. Too bad there isn't one for the A8! I'd get it.

pw (with electrical woes, good thing it's summer and don't need the lights until later in the day)

skiracer

Paul:
I agree that the Audi electrical diagrams are a real pain to decipher- I've been reading schematics for years too, and I much prefer a standard schematic to whatever it is that Audi uses. I'ts not Bentley's fault- Audi produces these things and have for many years (my 1987 5000 Q factory manual used the same electrical diagrams). You can decipher them, but it is a real pain tracing a single circuit through the whole mess. As for your problem, trace the various non-working circuits back to see if there is a common fuse or fuses- I've had a couple of fuses go out on me. Also, your thought on a common relay is a good one. Finding the physical location of any given relay in an A8 is a real hassle if you don't know specifically what it is called and can search the Bentley manual that way. I'd search my Bentley manual, but I'm in San Diego on business and away from my computer. I have access to the alldata database, so if you want me to search for something on that, let me know.

PaulW

Doug-

First of all, I stopped my whinning and figured out how the schematics work. I look at them every couple of years now, and it takes five or ten minutes (or an hour) to remember how they work. Got that straightened out.

I traced everything back that doesn't work to the "X" bus at the top of the page, there is a 30, 15, X and 31 bus that powers everything. I can't find what means what, but the "X" is switched power (ignition) and I believe that 30 is unswitched, etc.

However, I went back and looked at everything that doesn't work and it's all powered from the X bus, including steering wheel radio controls (but radio works, it's not from the X bus), headlights, turn signals, etc.

However, now I can't figure out how this X bus gets power, but it must be from some relay (glad I'm writing this, just figured that out). It's not the load reduction relay, there must be some way the car switches this power on and off with the ignition. If I can find that relay, I bet I can find the answer.

And I haven't even stepped out of my office yet! That's the way to troubleshoot the car. Let's see if I'm smart as I think I am. Usually I'm not.... :

skiracer

I there isn't a relay. I know that Audi runs full current through many of the switches in the steering column, and the X power may be simply switched by the ignition switch. I remember earlier discussions on this forum where the ignition switch was the source of problems. Do a search, maybe there is an answer. It could still be as simple as a fuse- don't forget to start your search there! Good luck!

PaulW

The relay panel is under the passenger's feet just to the right of the tunnel. You can see the fuse box on the right which is behind the little thumb screw thing in the passenger footwell.

<img src="http://pictureposter.audiworld.com/22012/relay_box2.jpg">

You can see the relay panel, it's below the carpet, you need to pull up the floor mat, then the carpet, and the relay panel has a piece of particle board over it with four screws holding it in place. Remove the screws and take off the cover.

<img src="http://pictureposter.audiworld.com/22012/relay_box.jpg">

You can see the central electric panel, with the six relays. From left to right, load reduction relay, dual horn relay (don't know what that is), headlight washer system relay, starting interlock relay, wiper/washer intermittent relay, fuel pump relay.

My relay was good, and as skiracer stated, it is the ignition switch. The ignition switch feeds 12VDC to the load reduction relay, which is the relay that powers all switched loads. Because the relay wasn't getting the 12VDC control power, it wasn't switching the relay. This includes all loads in my first post.

The reason why the A/C cut off last night was not fixed by cycling the ignition switch, the A/C turned back on as I drove away from a stop light because the fan wasn't on and driving it provided adequate cooling to the condenser. I pulled the codes this morning and found that it had triped on high discharge pressure (00801 - A/C Refigerant High Pressure Switch (F118)). This is because the fan could not switch to speed 2, and I don't know if it was running at all.

So I put the relay back in after testing it (okay, I went out and bought a new one too) and found that it was good. Did a search for the ignition switch on the archieves and found that it causes problems and must be turned back 1/4" after starting the car. Yes, this was the problem.

I can fiddle with the switch and find that if it is too far forward it turns all of this stuff off and if I put it back a little it turns everything on again. It's just the 12VDC signal to the "load reduction relay" (should be called "switched power relay") that is the problem through the switch.

Now to see what it will take to change out the ignition switch. Seems like a lot of people are going to be in for this sooner or later.

pw