So, cliffnotes version: I have working headlights now! I still need to wrap the harness, but I’ve verified everything works as it should.
Nothing here’s too groundbreaking, but just so it’s all documented in one place, here’s what I did to make it work. I’ll preface this by saying I’m not an expert by any means, so it’s totally possible (and probable) that I missed an easier way to do this.
To start, the materials list is as follows: (I bought enough wire so that I’d have plenty left over for other projects. You could get away with much less than what I used)
50 feet of 12-gauge Red wire and 14-gauge Brown wire. 30 feet of 12-gauge Yellow and 12-gauge White wire. 20 feet of 14-gauge Yellow and 14-gauge White wire. All of the above wire was purchased here, but feel free to source it from your favorite electrical supply provider. I also used 4x inline fuse holders, 4x 20A fuses, and 4x Hella weatherproof SPDT relay/kit. Then a standard variety of crimp connectors, ring terminals, and heat shrink. I found this Dorman kit to be pretty decent. Tools wise, you’ll need standard electrical tools – wire strippers, cutters, crimpers for open barrel connectors, a heat gun, and a multimeter. You can technically do this with 3 relays – one for both low beams and one for each high beam, but I went with one for each.
The new relays will be triggered from the original headlight wiring. Originally, the US-spec headlights are powered as follows:
Left – High beam (white wire/black stripe), Low beam (yellow wire/black stripe), Ground (brown)
Right – High beam (white wire), Low Beam (yellow wire), Ground (brown)
Cut off the original connector and strip the wire back. This was already done on my car (poorly) by the previous owner. PO had their relays located on the driver’s side of the car in the void underneath the AC condenser. I decided to do the same with mine.
To start, you’ll have to relocate the under-hood positive post originally mounted to the washer fluid bottle due to clearance issues with the headlights. I moved mine to the frame rail adjacent to it.
The relays should be wired as follows:
Terminal 30 to +12V source via inline fuse. (12-gauge Red wire)
Terminal 87 (relay output) to headlight. (12-gauge White or Yellow wire depending on high/low beam)
Terminal 85 to ground. I used a factory ground point on the passenger’s side of the car. You could also use the bumper mounts or make your own with a nutsert. (14-gauge Brown wire)
Terminal 86 (relay input/trigger). Extend the factory headlight wiring to this terminal using 14-gauge yellow or white wire depending on high/low beam).
I’m planning on wrapping my new wiring in Tesa Tape, although you could use Raychem-25 or something else if you prefer.
You can connect these to the headlights using standard uninsulated spade connectors. Verify the pinout of the headlight prior to making any connections. You should be able to see the wiring by popping off the Low beam cover. Mine was:
Ground (brown): Top (nearest to High Beam)
High (white): Bottom, beneath ground
Low (yellow): Bottom, next to High beam
The final pin is for the city light. I’m not using them for my setup.
The original connector from Audi is P/N 447 972 957, but these are NLA. There are also boots (Audi P/N 447 941 189) to go over these connectors, but they’re NLA as well. I’ve got a guy messing around with 3D printing these connectors and possibly the boots, but they’re not available yet.
After getting all of this put together, my right side low beam didn’t work. I found two separate issues, thankfully neither due to my wiring. First, the factory wiring for the passenger’s side headlight is broken somewhere between the headlight switch and the fusebox. Not a huge deal – I revamped the wiring to trigger both low beam relays from the driver’s side low beam wire. Next, I had a relay that was DOA. I ordered all four relays from the same source at the same time and received 3 Hellas and a knockoff. No surprise, the knockoff was bad. I verified this by swapping it with a (non-weatherproof) Bosch.
Once the new relay comes in, I’ll be good to clean up the wiring a bit, tape everything up, and send it. This is how the car sits as of yesterday afternoon. So. Freaking. Close.