HEADLIGHT SERVICES - Technical Info
Daniel Stern has the best technical documentation on the internet regarding vehicle lighting.
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Daniel Stern Technical
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Do I Need to Upgrade My Wiring?
Before you spend the money for upgraded bulbs, you might want to evaluate your wiring. First, with a good voltmeter, measure the
voltage output of your alternator. With the engine off, clip the leads of the voltmeter to the alternator and tie them back so they don't
get tangled in the belts or the fan. Start the engine and run it up to about 2000 rpm. Note the voltage and shut off the engine. Now
move the positive voltmeter lead to the back of the bulb, you may need to pierce the insulation to do this, or remove the bulb and put
the lead in the bulb socket. Leave the ground lead where it was. Now start the engine again and turn on your lights. Note the voltage,
shut off the engine, remove the test leads and if you needed to puncture insulation, seal it with silicone RTV. If your voltage drop is
over 1 volt, you have some repairs to make even before you upgrade your bulbs. Look for loose or corroded connections, loose or
corroded fuses or relays. Repair any problems. If you cannot get the voltage in an acceptable range, it is time to upgrade to a new
harness. It is HIGHLY RECCOMENDED that any vehicle that does not utilize relays in the headlamp switching circuit
upgrade to a harness.
Why Use Relays?
(The following is courtesy of Daniel Stern Lighting, www.danielsternlighting.com. Used by written permission.)
Power for the headlights is controlled by a switch on the dash. This is *not* a great place to tap into the system, for two reasons: The
headlamp switch uses tiny, high-resistance contacts to complete circuits, and the wire lengths required to run from the battery to the
dashboard and all the way out to the headlamps creates excessive resistive voltage drop, especially with the thin wires used in most
In many cases, the thin factory wires are inadequate even for the stock headlamp equipment. Headlamp bulb light output is severely
compromised with decreased voltage. The drop in light output is not linear, it is exponential with the power 3.4. For example, let's
consider a 9006 low beam bulb rated 1000 lumens at 12.8 Volts and plug in different voltages:
10.5V : 510 lumens
11.0V : 597 lumens
11.5V : 695 lumens
12.0V : 803 lumens
12.5V : 923 lumens
12.8V : 1000 lumens (Rated output voltage)
13.0V : 1054 lumens
13.5V : 1198 lumens
14.0V : 1356 lumens (Rated life voltage)
14.5V : 1528 lumens
The Europeans take a slightly more realistic with their voltage ratings; they consider output at 13.2v to be "100%". The loss curve
is the same, though. When operating voltage drops to 95 percent (12.54v), headlamp bulbs produce only 83 percent of their rated
light output. When voltage drops to 90 percent (11.88v), bulb output is only 67 percent of what it should be. And when voltage drops
to 85 percent (11.22v), bulb output is a paltry 53 percent of normal! It is much more common than you might think for factory
headlamp wiring/switch setups to produce this kind of voltage drop, especially once they're no longer brand new and the
connections have accumulated some corrosion and dirt.
For those in the Denver metro area we have a special tool that we use to test voltages and determine if the headlamps are
power or ground switched. Give us a call or send us an e-mail.