My 82 Coupe came stock with four rectangular DOT headlamps. I have two complaints about the stock lighting system. One is that the light on the road is fairly poor, especially when it's dark out. The other is that I don't like rectangular headlights - I think a round headlight casts a better defined, more useful beam.
The poor lighting is mostly a result of the wiring. (in 1985-7 Coupes and Four Thousands, it's also a result of the really horrible DOT aerodynamic lens and the 9004 bulb) The wiring of the headlight and switch circuits is woefully inadequate. The current for the headlights goes through the headlight switch, a half dozen connections, and about 20 feet of small gauge wire. This results in eventual damage to the switch and a gradual increase in series resistance to the bulbs, lowering their effective output quite a bit.
Another, more insidious wiring issue is that when one uses the "flash-to-pass" feature, all four high beam filaments are fed from the wire that brings power to the headlight switch for the instrument and parking lights. This results in the gradual degradation of three parts - the inside of the switch melts around that power terminal, eventually causing an intermittent parking light function (bad!); the harness socket to the switch melts around that same connection, which is mostly ugly but can weaken that connection; and in my case at least, the fuse box output to that circuit (E9) becomes intermittent due to melting of the plastic around the terminal.
So there are two separate projects to go through here. The first one is presented last, since it is supplementary to my main project, but it should be implemented on any well kept old Audi to improve even stock lighting. That is to rewire the headlight circuit through relays. The second one, which I have had a lot of fun playing around with, is to install a better headlight system.
I have a set of Hella 7" lenses with replaceable H4 bulbs installed in my '73 F250, and I've been really impressed with the low beam cut off and the quality of the beam pattern in general. My first thoughts were to emulate what I often see on the front of VW, a 7" outer lens with an inner 5-3/4" lens, used as a "driving light", or additional high beam. While the 7" lens would fit between my bumper and my hood, it would have been very difficult to mount them well and trim everything out so it didn't look butchered. I decided to use a dual 5-3/4" round setup. Hella lenses with H4 and H1 bulbs are available for the inner and outer position, and Audis and VWs used to have dual round headlights, so I could even stay with my theme oftrying to use OEM parts wherever possible on my car.
I used a set of the 1979 Audi 5000 headlight brackets. There is actually a picture of it in my owners manual, on the page full of "Genuine Audi Parts". Unfortunately the photo is small and of poor resolution or I would put it on the web site. I also scrounged up a set of the 1985-on style headlight mounting bracket, which holds the useless aerodynamic DOT lens and the nice corner marker light. I set these up on a spare car to see how they could be used together. All I had to do was attach the '79 part to the front of the '85 part with four little "mending plates" from the hardware store, and cut and bend back a bit of the vertical sheet metal below the hood pin locks to get it all to fit.
It was necessary to cut off a few little bits from each bracket, like the adjusting socket on the '85 and the original mounting tabs on the '79, but this was easy. I dismantled the mounting rings from the '79 bracket to remove all the plastic parts, welded the two sets of brackets together and sent them off to be sandblasted and powdercoated. When they came back I assembled them and fit it all together into my car.
I installed a set of four Hella lenses, and put 80/100w H4's in the outer and 100w H1's in the inner position. Very excellent lighting, and I've never been flashed on low beams. One thing I would suggest - it would make sense to use outer bulb mounting rangs on the inner bulb, get four H4 outer lenses, and use your steady supply of burnt out low beam H4's as highbeams in the inner position. I have a half dozen bulbs in my tool box with good 100w high beam filaments. It would be nice to have a use for them...
Now there is no way that the stock Audi wiring is going to support these fixtures without catching fire (see comments above). So I did what many others have done, I used several relays, triggered by the stock headlight wires, and getting (fused) power directly from the alternator terminal. This eliminates all the small gauge wiring and also provides a higher voltage to the lights, due to the elimination of all the series resistance. The basic heart of this part of the project, to trigger replays with the stock headlight wires and use them to switch power directly from the battery or alternator to the headlights, is something everyone with an older Audi should do. Don't forget the ground side - use fat wire and connect it to a good nearby chassis mounting point.
I used a 6 GA wire with a ring terminal running from the alternator to a car stereo style three fuse holder, which is tackily zip-tied to the lower radiator hose at this point. One fuse is for the low beams, one for left high beams and one for right high beams. The right high beam fuse also provides the juice for the foglight relay, since they won't be on at the same time. Then I ran 10 GA wire to the relays and to the high beams, with 12 GA to the low beams and fogs.
My relay set up is a little more complicated than most people would bother with, since I feel running 80 watt low beams could be anti-social under some conditions. I have wired an extra switch and two relays, that allow me to run the two low beam filaments in series, so each bulb only draws 20w. On this setting the light looks a lot like the stock system for 1985 on regular low beam! One relay switches the ground of the driver's side lights and the low beam relay to 12 volts (the two hot sides of the filaments are already connected by the normal low beam wire) and the other relay turns the system off if a high beam signal is present. It's not likely that I would use flash to pass while running my "city" lights, but if I did this would make it work normally, with no surprises (smoke, flames, etc.).
I find this setting to be invaluable when I use my fog lights. I bought some rather expensive PIAA 959i's, which are very well made, mount very solidly and have a nice sharp cutoff, using an H3 bulb. (They also come with a very nice harness and relay, but I didn't use most of that.) While they don't seem to put a lot of light on the road, under the conditions fog lights are actually needed, they are perfect. The "city" setting leaves the low beams on so the car can be located by other drivers, but cuts their output by 75% reducing glare from dense fog, heavy snow or torrential rain.
Due to the complexity of my switching needs created by the city light function, I had to use several Bosch relays in a "double switched" mode - that is, not only is the 12 volt side of the actuator coil switched, but so is the ground side. This created some interesting loops in my circuit which led to some unpredicted behaviour of the system at first. You see, while it takes about 8-9 volts to turn ON a Bosch relay, the relay won't switch OFF until the voltage drops to about 5 volts. So if two relay coils happen to be in series, with 12 volts at one end and and a ground at the other, and one is supposed to be OFF but was just ON a moment ago, it will stay ON since there is still about 6 volts running through its coil. I've found that the stock headlight harness wires not only provide 12 volts when they are on, but are grounded when they are off, so a wire intended as a 12 volt signal when it is on becomes a ground signal when it is off.
I solved this by using some 50 PIV 1 A diodes, which are cheap at Radio Shack, in the circuit at appropriate points. The relays I used, all parts bin stuff from old Audis, are not polarity sensitive - the coil will actuate if it has sufficient current in either direction. So the diodes limited operation to when current was flowing in my "intended" directions.
The relays are mounted in standard Bosch sockets (parts bin again) which are attached to a "bridge" like affair that came out of the fuse box area of a old 4000 diesel I had lying around. It is very neat, because it holds 5 relays in a row, and has a mounting hole at each end. I used brackets to attach each end to existing holes in the radiator support bracket and in the hood lock support sheet metal. I covered the assembly with the cut off bottom of an anti-freeze jug, to reduce the amount of road scuzz that gets to it. Someday I will arrange a neater, more weatherproof setup, but this works well for now. Over two years without a failure, anyway.