Headlights

Even those of us who have European lights fitted to our quattros recognise that Audi could have done better. Although the beam pattern thrown by Euro lights is much better (from a drivers point of view) than the beams produced by the lamps that were fitted for other market areas (the US DOT mandated lights used in the North American market are almost legendary), when fitted with standard 55/60w H4 & 55w H1 bulbs their performance on dark country roads falls short of that required to enable a driver to make full use of an Ur quattro.

Fitting high-power bulbs isn't as simple an option as it first appears to be, do this and the stock cables are then taken close to their maximum capacity. Audi used 1.5mm cables for the headligh circuit, which when new could have carried a continuous 13 amp current but now these cables have aged to the extent that the 8.3 amp current drawn by a 100w bulb is almost too much.

There are a number of solutions to this problem, one of which is to use the existing lighting circuit to control relays that supply power to the headlights directly from the alternator via an auxillary loom.

Please note that any cables used MUST be capable of carrying high continuous current.

100w = 8.3 amps

130w = 10.8 amps

I replaced all the headlight cables in my 1988 Ur quattro with 2mm cable - rated at 17.5 amp continuous current.

This basic circuit diagram shows one side of the lights (the right) and uses Audi European market cable colours. The left side lights use cables in the same colours but with black tracer strips.

The connector used for a H4 bulb is Audi part #161 941 165 A and is wired as shown. This view is of the cable entry side (rear) of the connector.

The H1 lamp has conical rubber sealing boot with a pair of short cables running through it. This pair of cables have a cylindrical socket fitted, part #813 971 956, and the headlight loom has matching part #813 971 955. Both these parts have now been replaced - new numbers are #813 972 926 and #813 972 923. There is also a side/city/parking light fitted to each lamp unit, using a 5w lamp fitted to a plastic bayonet type holder, part #855 941 669.

Of course, things aren't always that simple. Part of the way through the 1980s, all new vehicles for the UK market started to be fitted with dim-dip headlights. For this, Audi made a simple modification to the Day Running Lights circuit. In DRL mode, this circuit consists of a relay switched by the ignition controlling a permanently live feed. For the UK market, the live feed was changed to run from the lighting switch. If the switch is off, there's no power so the lights are off, if the switch is on, power is fed via a resistive wire to the lamps. This circuit is powered when the light switch is moved to the first position. A relay is switched which then supplies current to the headlights via a resistance equal in size to the headlight bulbs. Problem is, this 'dim-dip' supply will switch the auxillary relays so that the headlights are on at both positions of the light switch.

I tried a number of ways to retain the dim-dip function, one of which resulted in a rather amusing self-energising circuit which, unless the correct sequence was followed would leave the headlights on when the switch was off - even if the ignition was off too.

My first solution (a diode pack) worked for a while, but burnt out due to the current flow. Not wanting to risk an in-car fire, I've now re-worked the design using another relay, this one switched by the output from the dim-dip relay (a pink coloured 40amp unit mounted on the auxillary carrier behind the glove box in UK spec cars). Retaining the dim-dip function this way is possible if the whole loom is to be rebuilt with the headlight relays mounted on the auxillary relay carrier under the dashboard. If not, a considerable amount of additional cabling will be required.

The dim-dip resistance has to be changed to work correctly with high wattage bulbs - this is actually simpler than it sounds thanks to the way that Audi did things. The stock resistance consists of a length (approx 10m if I remember correctly) of high-impedance cable which should be shortened to provide the correct resistance for the new bulbs. The standard 60w bulb has a resistance of 2.4ohms, 100w bulbs have a resistance of 1.4ohms, so the cable had to be shortened by some 40%.

I've shown the dim-dip connection here in purple