Headlight Wiring Harness, is this good enough?

Matt Evans matt at mattevans.org
Sun Nov 14 19:21:43 EST 2004

For A/C wiring, 14ga is the NEC standard for short-medium runs of 15A or
less.  Most recent construction has it.

Extra new stuff is often using 12ga, as it is required for 20A.  When
re-wiring my houses I've put in 12GA for standard feeder circuits.  It's
harder to work with but the extra capacity is nice.

I think if I were going to all the effort to custom route and install new
wires in a car, I'd try 10GA for headlights.  It's going to be a pain no
matter how big the conductors are.  Might as well put in enough metal to
know you can handle any load you decide to put on there.  I don't know the
conductor requirements for DC loads, and I don't remember how stranded vs.
solid comes into play, but I'd probably go one size bigger than what you
think you need.  

One other comment - there is extra cost and complexity in running more
relays and fuses, but otoh, it is uh.. Non optimal if losing a single fuse
or single relay means you lose BOTH headlights.  The cats-meow setup is
separate fuses and relays for each primary bulb (i.e. 4 relays and 4 inline
fuses to cover drivers low, drivers high, pass low, pass high).  Separating
loads out like would let you get away with running more but smaller


> -----Original Message-----
> From: quattro-bounces at audifans.com 
> [mailto:quattro-bounces at audifans.com] On Behalf Of Larry C Leung
> Sent: Sunday, November 14, 2004 10:37 AM
> To: quattro at audifans.com
> Subject: Re: Headlight Wiring Harness, is this good enough?
> 200W/12V  ~ 17 Amps.
> To the best of my knowledge, the SUV harness comes with 30 A
> relays and fuses. It's the wires that are the limitation 
> here, the risk
> is melting insulation, which if they use the same wire as they used
> on my harness, is rated to 105C. 
> If you run things as designed, the standard Heavy Duty harness will
> be marginal, but acceptable, especially if you run the wires in the
> conduits
> (as you should, protects against abrasion). One suggestion to improve
> the margin if you use this set-up, run your wires carefully, 
> and cut-off
> the
> excess wire + conduit, thus reducing the resistance load. I am running
> the SUVLighting HD harness on my T44turbo (55/60W+55W high) and have
> had no problems, but I WON'T run 100W bulbs of any kind in 
> this system,
> there just isn't the margin in the wires needed to run these 
> for extended
> periods (quick flashes are okay).
> If you want to run the hi+lo (360W/12 ~ 30A) run together 
> mod, you will
>  the Super Heavy Duty. BTW, this isn't optically, the best idea. The
> concentration 
> of low beam light closer to the front of the car will tend to 
> draw your
> eye closer 
> into the car, not what you want to do if you need to run High 
> Beams. It
> brighter, but as I said, human nature tends to defeat the 
> purpose of the
> high beam, 
> AND there is no extra light being projected further ahead, 
> which is the
> purpose of 
> the high beam in the first place. 
> So, the drawbacks, bad lighting in terms of the human/optical system,
> extra current draw, and extra heat. The gains: more light to 
> blind other 
> people.
> LL - NY
> > Date: Sun, 14 Nov 2004 10:17:47 -0500
> > From: David <duandcc_forums at cox.net>
> > Subject: Headlight Wiring Harness, is this good enough?
> > To: <quattro at audifans.com>
> > Message-ID:
> >        
> <20041114151747.BDIP20686.lakermmtao07.cox.net at smtp.east.cox.net>
> > Content-Type: text/plain; charset=ISO-8859-1
> > 
> > I have a 1987 Audi COupe GT with Euro headlights (typ85 80 lights). 
> > Right now I am running with the stock wiring and 60/55w H4 bulbs. I 
> > want to run 100/80 watt bulbs and use a relayed wiring harness to 
> > lower voltage drop and lessen the chances of melting anyting. So, 
> > given that I want to run 100/80w H4s, are these pecs good enough?
> > 
> > "New & Improved Wire Harness features:
> > 
> > * 2 OEM Bosch/Tyco (Potter & Brumfield) 40 amp relays 
> (single & dual 
> > 87 outputs)
> > * Heavy Duty interlocking relay sockets with mounting tab
> > * Fusible link (slow reacting fuse protection) 12 heavy gauge 
> > automotive wiring
> > * Black split loom matches OEM to protect against heat and elements
> > * Male connector(s) to plug into existing headlight socket
> > * (2 or 4) new headlight sockets (depending on application)
> > 
> > The Heavy Duty models are 14 gauge wire.
> > 
> > They also offer a H4 Super Heavy Duty model is 12 gauge and uses 4 
> > relays. But it's quite a bit more expensive and if I don't need it, 
> > I will just get the Heavy Duty one...
> > 
> > Also, they offer a mod to their harnesses that allow you to keep 
> > your low beam on when you turn on the high beam. Good idea or bad? 
> > If I got it and was running the 100/80w bulbs, that wwould be 180w 
> > combined per bulb. Down sides? Too much heat? Too much current draw?
> > 
> > TIA!
> > 
> > Dave
> > 
> > 1987 Coupe GT Special Build 2.3 
> > All in SE VA
> > 
> _______________________________________________
> quattro mailing list
> quattro at audifans.com
> http://www.audifans.com/mailman/listinfo/quattro

More information about the quattro mailing list