Earths
Before attempting the following, cleaning up earths can make the headlights function properly, as dimming can be caused by dirty or corroded earths. The headlights earth along with just about everything else on the left hand 'A' post just under the fascia.
Remove the glovebox (RHD) or the driver's knee panel (LHD) and the earth connections are there on the left hand A-pillar. Depending on the year of manufacture and how the Ur-q sparkies were feeling at the time, the earths will either be bolted directly to the body or via spade terminals onto an earthing block.
Installing Relays
The concept is to use relays to offload the original wiring (which pulled all its power through the headlight switch!) and produce a (fused) heavy duty feed from somewhere, preferably duplicated left/right if you don't fancy losing both lights due to a single failure (redundancy protection). The original wiring will have decreased ability to handle current due to age. Uprating headlight bulbs requires cable with higher capacity.
This upgrade is well worth doing. The result is:
a) The weak and feeble Audi headlight switch stands a chance of surviving.
b) About 1.2V more at the headlights.
The downside is bulb life may be shortened, although not by very much. You can be silly and fit Ring R590 100W/165W bulbs - as long as you replace the headlight lenses no one will ever complain.
Obtain a set of headlight connectors from a scrap car - most junkyards will let you cut the connectors off the loom, since it's one of the looms there is almost no demand for. It is possible to leave the original loom untouched, in case a future owner wants to restore originality. The original connectors are just detached from the lights and left in place - one of them is then connected to the relays to drive them, but can be unplugged whenever required.
Take the positive feed off the back of the alternator - it has an excellent thick cable to the battery, so it's live whether or not the engine is running. Fit an in-line fuse in this cable near to the alternator. Unfused cables in the front of a car are a very likely source of fire if the car has a minor front end shunt for instance, caused by an unfused positive wire shorting to a negative wire or the vehicle’s body.
Use the chassis ground on the right engine mount - there's already a huge braided cable connected to that.
The relays are usually mounted next to the radiator, under the cardboard cover.
The BR Motorsport loom (originally intended for a VW Golf) used three headlight connectors - one had some strips of copper hoved into it so it could be mated with one of the car's connectors to drive the relays.
The following point only applies to the WR-engine Ur-quattro with digital dash (1984-87). If you want to retain the bulb warning function provided by the digital dash, you have to run the dipped beam current through the controller and take the "K" pin back to the auxiliary relay panel. The controller has to be moved from the auxiliary relay panel out to where the relays are situated.
WARNING:
THE COMMON 12V AUTOMOTIVE BATTERY WILL PROVIDE ENOUGH CURRENT (HUNDREDS OF AMPS) TO CAUSE A SEVERE ELECTRICAL FIRE IF ANY UN-FUSED +12V (Positive Battery Connection) WIRE IS SHORTED TO THE VEHICLE’S BODY (Negative Battery Terminal)
IF YOU ARE UNFAMILIAR WITH MODIFYING THE ELECTRICAL WIRING ON YOUR VEHICLE, YOU SHOULD CONSULT A REPUTABLE REPAIR SHOP FOR ASSISTANCE WITH THIS TYPE OF WORK.
Acknowledgements: Edited posts from quattroforum.com
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