Kday, making a harness to relay my headlights.

20VT90q · 10-24-2006, 08:34 PM

I need to know what kind of relays to get (using two, one for highs, and one for lows). I notice some people use the 30w and some use the 40w. Which one? I also need to know if I should get the relays with a diode or resistor or both? I'm thinking two HL87402 is best. Also, can I use the brown wire from the stock wiring harness to ground out the headlights or should I run sperate wires to the headlights for that?

TIA

Relays

TabulaRasa · 10-25-2006, 03:46 AM

Don't waste your time with halogens.

kday · 10-25-2006, 04:16 AM

A 100 watt bulb draws about 100w/12v=8.5ish amps.

You can use the brown wire for the low side of the relay coil, sure. Run a fat new one for the lamps.

The diode serves to prevent the inductive spike caused by turning off the relay coil (the same principle ignition coils generate sparks by). Use the diode version -- better to avoid polluting your electrical system. The resistor does the same job, but not as well.

The reason all relays don't have the built in diode is because the contacts will open more slowly with the diode than without. This can cause a problem when switching large loads (contact arcing) and potentially some applications need a quicker switching time. But for headlights it doesn't matter. Use the diode one.

SilberUrS6 · 10-25-2006, 04:53 AM

Second-best mod to make on the car, and best bang-for-the-buck mod, by a long shot.

connell · 10-25-2006, 06:32 AM

20VT90q · 10-25-2006, 08:50 AM

These are e-codes.

20VT90q · 10-25-2006, 08:51 AM

Blake@NWAutoSalon · 10-25-2006, 11:26 AM

I dont feel like I can see anything here at night without my highs on...

SilberUrS6 · 10-25-2006, 12:12 PM

Especially the rear.

Speaking of annoying - when I was following you, how was the glare?

Blake@NWAutoSalon · 10-25-2006, 01:43 PM

I must not have noticed.

10-25-2006, 03:46 AM	#2
TabulaRasa Member Garage is empty, add now Join Date: Apr 2001 Posts: 6,009	I'm running 35 watt xenons on stock wiring. Don't waste your time with halogens. __________________ Original S4/S6 FAQ>

10-25-2006, 04:16 AM	#3
kday AudiWorld Super User Garage is empty, add now Join Date: Nov 2003 Posts: 5,247	Either 30 amp or 40 amp would be okay. A 100 watt bulb draws about 100w/12v=8.5ish amps. You can use the brown wire for the low side of the relay coil, sure. Run a fat new one for the lamps. The diode serves to prevent the inductive spike caused by turning off the relay coil (the same principle ignition coils generate sparks by). Use the diode version -- better to avoid polluting your electrical system. The resistor does the same job, but not as well. The reason all relays don't have the built in diode is because the contacts will open more slowly with the diode than without. This can cause a problem when switching large loads (contact arcing) and potentially some applications need a quicker switching time. But for headlights it doesn't matter. Use the diode one. __________________ 1994 S4 with stuff 1996 A6q Avant with no stuff 1990 Miata with a little stuff

10-25-2006, 04:53 AM	#4
SilberUrS6 AudiWorld Super User Garage is empty, add now Join Date: Mar 2006 Posts: 11,235	Ding! Second-best mod to make on the car, and best bang-for-the-buck mod, by a long shot.

10-25-2006, 06:32 AM	#5
connell AudiWorld Member Garage is empty, add now Join Date: Jun 2004 Posts: 382	double ding!

10-25-2006, 08:50 AM	#6
20VT90q AudiWorld Super User Garage is empty, add now Join Date: Sep 2002 Posts: 5,820	I'm going 100w or 130w for the Highs and Hella H1 or HK HIDS for the lows. These are e-codes. __________________ <U>Project '93 Urs4</U> -8/'92 Build Date ~Rear Sway/Suspension~ -Suspicion of a chip (cut carpet) ON THE BED: H&R's, '92 trip computer cluster, Sport Wheel, TDS-1, E-code Headlights, Euro Bumper, A8 Interior Auto-Dim Mirror <U>'90 20v 90q:</U> -RS2 Headlights -16" Borbets -Manual Climate Swap -Concert Headunit -Quattro Scripts (Auto to manual swap) -034 Injectors -B4 Hood Conversion <U>'93 100CS:</U> -Bad Headgaskets/leaky steering rack -FWD/Auto Garbage

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10-25-2006, 08:51 AM	#7
20VT90q AudiWorld Super User Garage is empty, add now Join Date: Sep 2002 Posts: 5,820	Thanks for the answers! __________________ <U>Project '93 Urs4</U> -8/'92 Build Date ~Rear Sway/Suspension~ -Suspicion of a chip (cut carpet) ON THE BED: H&R's, '92 trip computer cluster, Sport Wheel, TDS-1, E-code Headlights, Euro Bumper, A8 Interior Auto-Dim Mirror <U>'90 20v 90q:</U> -RS2 Headlights -16" Borbets -Manual Climate Swap -Concert Headunit -Quattro Scripts (Auto to manual swap) -034 Injectors -B4 Hood Conversion <U>'93 100CS:</U> -Bad Headgaskets/leaky steering rack -FWD/Auto Garbage

10-25-2006, 11:26 AM	#8
Blake@NWAutoSalon Elder Member Garage is empty, add now Join Date: May 2003 Posts: 11,096	I need to get some HID's very soon. I dont feel like I can see anything here at night without my highs on... __________________ Current: -1995.5 Audi S6 Europa Blue/Ecru MTM Stg 1+ and Samcos, 18" B6 S4 wheels, 3" Stainless Downpipe and Exhaust from 034 (1 Muffler, No Cat) FOR SALE 1991 Audi 200 20VT Pearl/Platinum 3" Samcos and 17" B5 S4 Wheels, 20% Tint, G60 Conversion -1969 Lincoln Continental 4 Dr Hardtop Black on Black Glove Leather 34k original miles on 22" Wirespokes, Lowered, Lazy eyes and window tint. -1990 Audi Coupe Quattro Tornado Red Standalone 20VT Built Bottom End, GT35/40R, Internal Wastegate, Tial BOV, Fidanza Flywheel, Stage 4 Clutch, RS2 Headlights (w/HIDz), RS2 Front Bumper turn signals and Porsche Airduct/Fogs and Kamei Sport mesh, Porsche Aero Mirrors, Bilstien Sport and GC Coilovers, B4 Hood conversion with Kamei Sport Grill, Blacked out S2 taillights, White Faced Gauges, S2 sport steering wheel, New paintjob with ghosted Audi rings Dearly Departed: -1986 Audi 5000S Turbo FWD 5Spd -1993 Audi UrS4 Emerald on Ecru //RSDueced -1991 Audi 200 20VT Cyclamen with Black Leather and just a few mods :-) -1982 Audi Coupe Surinam Metallic w/brown tweed int. -1987 "Audi 4000000 "turbo" quattro CS", Best car EVAR! -1986 Audi 5000S R.I.P (10V Turbo Donor) -1990 Audi 90 FWD 3-Spd Auto *Secretary of Transportation (Unofficial 80/90 Cabinet)

10-25-2006, 12:12 PM	#9
SilberUrS6 AudiWorld Super User Garage is empty, add now Join Date: Mar 2006 Posts: 11,235	And running foglamps is very annoying to other drivers. Especially the rear. Speaking of annoying - when I was following you, how was the glare?

10-25-2006, 01:43 PM	#10
Blake@NWAutoSalon Elder Member Garage is empty, add now Join Date: May 2003 Posts: 11,096	When were you following me? I must not have noticed. __________________ Current: -1995.5 Audi S6 Europa Blue/Ecru MTM Stg 1+ and Samcos, 18" B6 S4 wheels, 3" Stainless Downpipe and Exhaust from 034 (1 Muffler, No Cat) FOR SALE 1991 Audi 200 20VT Pearl/Platinum 3" Samcos and 17" B5 S4 Wheels, 20% Tint, G60 Conversion -1969 Lincoln Continental 4 Dr Hardtop Black on Black Glove Leather 34k original miles on 22" Wirespokes, Lowered, Lazy eyes and window tint. -1990 Audi Coupe Quattro Tornado Red Standalone 20VT Built Bottom End, GT35/40R, Internal Wastegate, Tial BOV, Fidanza Flywheel, Stage 4 Clutch, RS2 Headlights (w/HIDz), RS2 Front Bumper turn signals and Porsche Airduct/Fogs and Kamei Sport mesh, Porsche Aero Mirrors, Bilstien Sport and GC Coilovers, B4 Hood conversion with Kamei Sport Grill, Blacked out S2 taillights, White Faced Gauges, S2 sport steering wheel, New paintjob with ghosted Audi rings Dearly Departed: -1986 Audi 5000S Turbo FWD 5Spd -1993 Audi UrS4 Emerald on Ecru //RSDueced -1991 Audi 200 20VT Cyclamen with Black Leather and just a few mods :-) -1982 Audi Coupe Surinam Metallic w/brown tweed int. -1987 "Audi 4000000 "turbo" quattro CS", Best car EVAR! -1986 Audi 5000S R.I.P (10V Turbo Donor) -1990 Audi 90 FWD 3-Spd Auto *Secretary of Transportation (Unofficial 80/90 Cabinet)

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