Brighter Headlights

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Visitor # 61530 since 28.AUG.2001


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Halogen Headlight Swap:

The stock 6054 sealed beam headlights in my '82 Caddy were pretty dismal. I remember more than one time getting out to see if they had burned out as I could not see any light on the road in front of me (unfortunately they were not burned out :). So, I decided to swap them out for a halogen lamp. For a while I used a set of Hella Vision Plus, H4 halogen replacement lamps. They worked great, but later I grabbed them and installed them in my 4x4 Toyota (since I tend to drive that in bad weather and very dark backcountry roads).

For the Caddy, I decided to get something different. I picked up a set of sealed beam halogen Philips Color Clear lights. I chose them mainly for the black-out color when they are off, they sort of blend into the black grill on my Caddy (see photo below). Also, the black grill inside the housing really cuts down on glare and the lights work just fine for my needs. The only drawback of the internal grill is that it cuts down on the light output a bit, so the extra current I would get with a headlight relay kit is just the ticket. These lights are no longer made, but I have my working pair and a spare lamp, so I'll make do with them for now. With a sealed beam lamp, upgrading the bulb is not an option, so increasing the power to the light bulb is the only way to go.

The Philips Color Clear headlights apparently are no longer available and I don't know where to get them.

Front view, '82 Caddy, blacked out headlights

H4 Conversion:

If you want to convert from sealed beams to the H4 type headlights (w/ separate bulbs), you'll want a 200mm rectangular H4 lamp. With H4 headlights, you have many choices of lamp designs (DOT and E-code light patterns) as well as countless choices of bulb wattages and color temperatures.

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Upgraded Headlight Wiring Harness:

After installing a headlight relay kit in my 4Runner, and seeing the skimpy stock wiring and convoluted path that the headlight current takes, I decided it was time to upgrade the system wiring. To re-iterate, this was done on the stock, factory headlight wiring harness, I had made no modifications to it, aside from replacing the old sealed beams with the some Philips Color Clear sealed beam halogen headlights. Besides improving the light output, the relays will take the load of switching the high current of the headlights off the old factory headlight switch. This part is no longer available from VW so if it wears out, the junkyard is the only option to replace it. And if I ever do decide to upgrade to higher output lamps, I'm all set!

The H4 bulb has 2 filaments, one for low and one for high beam. It has 3 wires arranged in a "U" shape, 2 vertical, one horizontal.

So armed with the knowledge that VW headlights operated on a switched power system (i.e. the common connection of the bulbs is grounded and the power is supplied to one or the other filament to light the bulb), and that I use H4 style headlights in my '82 Caddy, I found a nice looking and well designed wiring harness kit that seemed to fit my needs, it supports 2 - H4 style headlights (one on each side) and works off of the switched power system that VW uses:

Pictured above is a 9004-style, switched power harness, but its very similar to the H4 harness I used. The blue connector looks like the back of a headlight bulb and you simply connect one of the existing headlight connectors to it. The harness is designed to accomodate headlight separations of nearly 6 ft. so should fit most common vehicles.

So on to the installation:

Male and Female H4 Connectors
A: Headlight Wiring Harness Connection
Note: The H4 style connector (3-wire)

This connection (A) supplies the control power to the two relays in the new harness, you just plug one of the stock (dirty yellow colored) headlight connectors (female H4) into the (bright yellow) mating connector (male H4) on the new harness. It can only go in one way and there is only one male H4 connector, so its hard to get this step wrong! Since this connector is close to the relays, which in turn have to be close to the power source. its best to use the headlight connector nearest where you intend to tap into power. Since I tapped into power at the engine fuse block, I used the passenger side light, your installation may be different. The 9004 harness installing is similar, just match up the male and female 9004 connectors in the same manner as the H4 connectors.

New Relays and Fuseblock Connection New and Old H4 Connectors
B: New Relays and
Fuse Block Connection
C: Stock H4 Connector (unused)
New H4 Connector Installed

Then you connect the power leads in one of sevearal ways, depending on your preferences. For a "quick and dirty" installation, you can suiply attach the ring terminals on the ends of the two power wires directly to the + terminal on the battery. There are built-in fusible links in those wires for electrical protection. Or for a cleaner installation, with a fuse (I used a single 30A fuse in my auxiliary fuse block, but two separate 20A fuses would also work well) to power (picture B - if no fuse block handy, you can run a fused wire off the battery or off the engine fuse box as needed). For a fused installation, you'll likely want to cut off the ring terminals and either splice both wires together (for a single fuse installation) or splice on additional wire (if needed) to reach your fuse block and then attach a suitable connector to attach to that fuse block.

Then attach the two ground connections to the frame or body near by the headlights. I found a couple of body bolts that were a good ground points. Finally, plug the two new connectors into the headlights (C) and you are done.

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Try before you buy, or a simple health check for your stock wiring:

Measuring Headlight Voltage
Measuring Headlight

Your results may vary so you should really consider testing the voltage, as shown above, on your own headlights. This way you can see ahead of time what sort of "room for improvement" you have. It is important to do this test under load and compare the voltage across the headlight connector vs. the battery voltage. If you are seeing your headlight voltage is within about 0.5 volts of the battery, you are already "doing pretty darn good". Not a lot of room to improve and you are probably getting 95% of the light out of your headlights that is possible and you probably would not even notice a 5% increase if you were even able to get it. So, you would probably be better off not "upgrading" something that is already working optimally (or as they say "if it ain't broke, don't fix it"). Note that human eyes are not terribly sensitive to small increases in light output. For example, it is probably hard to detect a 20% light increase. Also, the increased light output you will see is often in the form of a more uniform light pattern (that is the dimmer areas are now closer in brightness to the brighter spots) rather than the bright areas being brighter. This results in a more useable light pattern (i.e. more light on the road) for driving, which after all is the whole point of the headlights. Also, if you decide you want to upgrade the headlight wiring, you will also know if you have a switched ground or switched power setup.

As it turns out, light output is approximately proprotional to the 4th power of the voltage across the filaments in the bulb. If the higher math is not your thing, have a look at the graph below. It shows light output for a typical halogen lamp on the vertical scale vs. lamp voltage across the horizontal scale. Compare the light output at your measured voltage to that you would see at your battery voltage. To do that, draw a line up at your measure voltage to where it intersects the red line on the graph. Then from that point, draw a horizontal line across to the light output (Lumens) scale and estimate the value. Repeat for the battery voltage and compare the two light outputs.

Light Output vs. Voltage
Plot of Light Output vs. Lamp Voltage for a typical halogen headlight lamp


One thing to consider with halogen bulbs is that they last longer when run as hot as possible. The halogen gas inside the lamp combines with the (tungsten) metal ions that "boil" off the filament during operation and forms a tungsten-halide compound. This tungsten-halide circulates inside the bulb and when it hits the hot filament, it decomposes and redeposits the tungsten on the filament and releases the halogen back in gaseous form. This helps to keep the the light output more constant over time (since the tungsten does not deposit on the inside of the glass envelope) and by replenishing the tungsten on the filament, it does not burn out as fast. This chemical reaction takes place at temperatures in the 500°F-750°F range and when the bulb operates at the proper temperature, it can last many times longer than a normal incandescent bulb. However, when a halogen bulb runs too cool, this mechanism doesn't work as well so the bulb burns out faster and give less light. In fact, since halogen lamps and filaments tend to be smaller than normal incandescent bulbs, they can burn out much faster. This is sort of the opposite for normal incandescent light bulbs, they generally last longer at lower voltages. So, for maximum lifetime out of your fancy halogen headlight bulbs, you want to run the lamps as close to their full rated voltage as possible.

On the other hand, all the wiring harness is doing is supplying more of the system voltage that the bulb was designed for to the bulb. You will not get any more voltage than the vehicle's charging system is capable of delivering even if you used huge cables or even super conducting wires. So in no way will the harness lead to a light burning out from too much voltage. That is if your charging system puts out say 13.8 volts DC at the alternator, there is no way to get more than that 13.8 volts to the light bulb with any combination of (passive) wires and relays, all you can hope to do is to lose as little as possible of that 13.8 volts between the source (the alternator) and the load (the light bulb).

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So how well does the system work? In my opinion, it works great. The relays are socketed for easy replacement if needed, and I like the fact that I can revert to stock just by swapping back to the old headlight connectors, handy if a relay dies on a long road trip, or I want to move the harness to a new vehicle. All the wires are run in protective looms, and everything is straight point-to-point connections, no splices or other mid-wire breaks.

For a quick test of how effective the harness is, I used a volt meter across the headlight bulb to measure the actual voltage drop at the filaments (or as close as I can get to them:). With the stock harness, I measured 10.6v and with the new harness, I got 12.6v. May not seem like a huge difference, but light output is shown on the above graph and is about 80% more light, for the same bulb no less. Pretty good for a $35.00 harness and a few minutes of installation time. In fact, the light output of the sealed beam halogen head lamps I had in there was increased to the point that I decided it was not worth it to change the lamps out, at least until those sealed beams burned out. As they say, "if it ain't broke, don't fix it!"

The above voltage was re-measured with a fully charged battery and engine running and I found the system voltage to be 13.6v. and the lamp voltage to be around 13.2v.

One thing to consider with halogen bulbs is that they last longer when run as hot as possible. The halogen gas inside the lamp forces the metal ions back towards the filament to redeposit them and increase the light output. When run too cool, this mechanism doesn't work as well so the bulbs burn out faster and give less light. This is sort of the opposite for normal light bulbs, they generally last longer at lower voltages. On the other hand, all the wiring harness is doing is supplying more of the system voltage that the bulb was designed for to the bulb. You will not get any more voltage than the vehicle's charging system is capable of delivering even if you used huge cables or even super conducting wires. So in no way will the harness lead to a light burning out from too much voltage.

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Which wiring harness do you need?

H4-style connectors 9004-style connectors
A: H4-style Connectors B: 9004-style Connectors

Bottom line:

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On-line Ordering:

The H4 and 9004 headlight wiring harnesses are currently out of stock. Feel free to contact Missing LinkZ if interested in more info. We'll update the web page when we have a new harness design ready for purchase.