RE: Lighting questions

["Buchholz, Steven" <Steven.Buchholz@kla-tencor.com>]

> >Scott, IME, stock wiring is simply not heavy enough to carry such loads 
> for
> >any length of time
> 
> Why?  I've followed threads endlessly, downloaded proposed wiring 
> diagrams from other sites, but never seen an analysis of stock wiring.  
> My high beams are powered from the wimpy switch by one 12 Ga. wire, then 
> two fuses feed two 14 Ga. wires that go to the bulbs, then two 14 Ga. 
> wires to ground.  I'm on the road and can't look this up, but I believe 
> 14 Ga. wires are rated for 15 amp applications (?).  That's about 200 
> watts at normal alternator voltage per wire, plus an unknown safety 
> factor (usually pretty high for automotive).  That rating also takes 
> into account momentary spikes.  Hella cites up to ten times the power 
> rating for their bulbs on start up, other applications may draw even 
> more, and the wires are rated for those normal applications.  What about 
> the connections?  These same connectors are used for much higher loads 
> elsewhere.  I agree there are line losses, after ten feet of wire you 
> should jump to the next Ga. wire, and I'm close to ten feet.  My bulbs 
> may run a little cooler and last a lot longer.
> 
> How much difference does heavier wiring make in headlight performance?  
> No one has cited any measurements, just subjective opinions.  I spent a 
> 
Perhaps not recently, but I have seen people post the voltage improvement at
the lights ... my hazy recollection is that the number was something like 2
volts ... which would be about a 15% increase.  

I would not be concerned too much about the instantaneous onrush current ...
the problem with underrated conductors is usually resistive heating, which
occurs over a longer period of time.  

I cannot speak to the improvements in lighting efficiency afforded by the
higher voltage to the bulbs ... but the lights should be brighter and
putting out a whiter light.  Over time contacts develop resistance, when you
consider how many connectors and switches that the current for the bulbs has
to pass you can see that the effect is multiplied, further reducing the
voltage at the bulbs ... and creating even more heat at the connectors and
switches!  Eventually you can get a situation of positive feedback, where
the resistance causes the heating, which causes the resistance to increase
... until you melt the connector housing and create an open circuit.  

In my mind one of the major benefits of installing relays and beefed-up wire
for the headlights is that it eliminates the high current and the related
heat int the wiring harnesses that pass through the firewall and up the
steering column to the switch.  This eliminates one possible source for an
underdash fire or meltdown and should make the headlight switch last longer.
The other benefit is that it will allow higher wattage bulbs to be used
without overtaxing the stock wiring ...

This recommendation does not apply only to the headlamps ... the ignition
start switch and fuel pump relay circuits can benefit from the addition of a
"load reduction" relay in many cases as well ...

HTH!
Steve Buchholz
San Jose, CA (USA)