Wiring Resources

Daniel Stern Lighting
Daniel Stern is THE source for vehicle lighting. His website is full of information on lighting upgrades and improvements.
Daniel Stern Tech
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The 12 Volt
No real info on headlights but lots of information on vehicle wiring.
The 12 volt
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Basic Car Audio Electronics
Again, no real info on headlights but lots of information on vehicle wiring. Excellent functioning graphics on wiring princilpes and components.
Basic Car Audio Electronics
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Universal Power-Switched Premium-Plus Wiring Harness - Dual H4, 9003, 6024, 6054 Headlamps
We offer complete custom designed wiring harnesses for headlamp conversions with standard ground or switched ground (for Japanese cars and trucks, and some newer Chrysler and Jeep products) to meet your specific needs. These harnesses are built to your order. All harnesses are made in the USA.

These wiring harnesses are a simple solution to upgrading your headlamp and auxiliary lamp wiring. 12 gauge wire is used for all high current circuits. Multi-conductor wire is used for parallel runs.

Connectors simply plug into your Original Equipment connector and your upgraded bulbs. The only other connections are at the car battery. Includes separate relays for high and low beams mounted on a relay base designed for mounting inside the engine compartment. NO CUTTING OF YOUR EXISTING WIRING HARNESS IS REQUIRED! If at some time in the future you want to remove your custom harness, no evidence will be left behind. This is truly plug-and-play.

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 RECOMMENDED 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 factory installations.

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:
We offer Prmmium Universal Harnesess and Custom Harnesses for certain vehicles. Our custom harnesses are currently available for the 3rd Gen (1995-2002) Toyota 4Runner and Jeep Cherokee XJ (1986-2001).

For the 2005-2015 Toyota Tacoma (without DRLs) use our Universal Power-Switched Premium-Plus harness found below.**

- Do I need to upgrade my wiring?
- Universal Wiring Harnesses - Premium-Plus, Power Switched
- Custom Wiring Harnesses - Toyota 4Runner, Jeep Cherokee
- Wiring Resources

Get Maximum Voltage to Your Headlamps!
PREMIUM-PLUS Power-Switched Headlamp Wiring Harness for Vehicles with two H4, 9003, 6024, 6054 Headlamps
• 12 AWG wire to headlamps
• High-temperature "CERAMIC" headlamp bulb connectors
• Two superior quality 40 amp Bosch/Tyco relays mount within 18" of battery.
• Fused dual circuit 12 AWG GPT wire with ring terminals bolt to battery positive (+).
• 10 AWG GPT wire ring terminal bolts to battery negative (-).
• 18" 16 AWG GPT trigger cable plugs into stock headlamp connector.
• 12 AWG GPT wire to headlamp bulbs (24" to near side, 73" to far side).
• All connectors crimped and soldered.
Universal Power-Switched Premium-Plus Wiring Harnes for conventionally Switched Power vehicles with two H4 lamps. $109.50.
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 are 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.