As people add turn signals to their old street rod or as they do more major modifications by changing or adding lights, they often become confused about the circuitry of the taillights. For full visibility at the rear of the vehicle we need three distinct functions: (1) the taillights that allow us to be seen from the rear, (2) the brake lights that notify drivers behind us that we are stopping or slowing down, and (3) the turn signals that advise of turns and lane changes. Confusion arises because of the numerous ways to achieve the end results and in making sure that you have the right combination of parts that work together.

The straightforward way to get three different functions would be with three different bulbs either within each lamp housing or clustered on each back fender. This is exactly what is done with many European and Japanese cars as well as many newer Detroit vehicles. The turn signal lenses may be either red or amber to stand out, and the signal flashes independently of the other two lights. This approach has the advantage of keeping both brake lights working even when the signals flash. It also makes for a very simple turn signal switch - a three-position switch (left turn, off, right turn). The down side is that it takes a bit more wire and a lot more space. Can you visualize 6 teardrop taillights across the back end of a '34?

So how do we reduce the number of bulbs? Let's have a two-for-one sale. By putting two filaments into a single bulb, like an 1157 bulb for example, we can reduce space and still maintain three distinct functions. The turn signal bulb is still often left as a separate function so as to retain all of the benefits we listed before. Then the taillight and brake light become the two different filaments in the 1157. We still have three light filaments to give us our three functions, but we've saved 33% of the taillight housing space needed. Unfortunately, it still leaves us with 4 teardrops across the back end of our '34.

It would really be nice if we could further reduce the number of bulbs and get down to one per side. To achieve this we need to, somehow, "combine" two of the functions so that they can be done by the same bulb filament. In that way, two filaments give three functions. If the brake lights are ON, we really don't need the taillights because we will be seen anyway. But combining those two functions won't work because using the same filament for brake lights and taillights would make them the same brightness. We would push on the brakes and it would look exactly the same as with just the taillights on. The same would be true trying to combine the taillights and the turn signals. So the only two functions that we can combine are the brake light and the turn signal because they are the same bright­ness and could use the same bulb filament.

That combination still has a draw back. If we have one of the turn signals on and flashing, and then we push on the brake lights, the brake light will provide a con­stant voltage to that filament and cancel out (or override) the flashing turn signal. To fix this brake light over­ride, we need some mechanism that will detect when a turn signal is ON and that will not allow the brake light to feed that light. So, for example, while the right signal flashes, the left brake light works but the right turn signal isn't overridden by the brake. This way a specific bulb can be a taillight and brake light -or- a taillight and turn signal, but not both at the same time.

Detroit tackled this problem when they first introduced turn signal to cars. They had been using 1157 dual filament bulbs for years to give them taillights and brake lights in one single bulb. And, for good reason, they wanted to keep that ability. So when they de­signed the new switch for the turn signals, they built the brake light override mechanism in as part of the mechanical turn signal switch. And since that made the whole switch rather large, they hid it inside the new, larger steering column. This minimized the changes caused by the addition - new steering col­umn with switch, separate feed wires for each rear brake/turn filament. The taillights and license plate light could still be fed by just one jumpered wire. Great! Now we're down to just two teardrops!

But when we retrofit our '34 street rod with a new turn signal switch, we may not want to change the steering column just to get the switch with override capability. A nice stiletto column was more to our liking. The solution is to achieve the same results elec­trically, which can be done with a properly wired group of relays.

So, What is all this Fuss about LED Taillights?
For all of the above discussion, we have been focusing on taillight bulbs such as the 1157. But when something new and different comes along, street rodders are going to jump all over it. Right now, that new and different and better item is the LED. But what is an LED and why is it so different and better than regular incandescent bulbs?

What is an LED, anyway?
An LED (which is usually pronounced as the letters L.E.D. but also is used as an acronym pronounced like the metal, "lead") is a Light Emitting Diode - a semiconductor device that emits light when a volt­age is applied (typically 2.1 volts dc). Explaining why that happens would require an education in electri­cal engineering and atomic shell theory which we will bypass. Instead let's just call it magic! But it's really neat magic. When they are properly grouped into a cluster or strip, LED's make great lights and have become the favorite choice for center high mount third brake lights in both OEM and aftermar-ket applications. Individual LED's also make great indicator lights for both automotive use and home electronics products. Since an individual LED is usually a 2.1 volt item, in order to use it as an indicator, a resistor must be added. Most LED's sold as indicators already have the resistor installed for 12 vdc use. When put into clusters or strips, 4 or 5 LED's plus a smaller resistor are wired in series to give the correct voltage drop for 12 vdc.

What advantage is an LED Taillight/Brake light?
An LED produces more light from less amperage and voltage, comes on almost instantaneously, creates nil heat compared to an incandescent bulb and typically lasts 100,000 hours when used within its correct voltage range. That's what makes them different and better. Less amperage use helps to relieve the strain placed on car electrical systems. An LED's faster response time means that drivers behind us know more quickly that we are stopping. Their low heat allows them to be located in tight spots. And their long life costs less over the life of the car.

O.K. There must be a catch. What's wrong with LED's?
Well, it's not that they have anything wrong but that they are different than an incandescent bulb, (like an 1157) and we have to realize that in order to use them properly.

First, LED's give out one color of light (one specific wavelength) - it's part of that magic thing we mentioned. So they come in red, yellow, green, etc., but not in a true white which is actually not a light color but light of all colors mixed together. That is why they don't work well with blue-dots, red light going through a blue lens gives you next to nothing. White LED's are usually achieved by using a blue LED that is coated with an iridescent material to give a near white ap­pearance. This is also why LED's are used with a clear lens or one that matches the LED color, red LED's in a red plastic housing, amber in amber, etc., this assures maximum transmission of light through the lens.

Second - As opposed to incandescent bulbs, LED's are very directional and are used with a lens (which is actually part of the LED in most cases) to get some spreading of the light. A 20-degree spread LED is common. As a result, to use LED's for a brake light or full taillight, the LED's must point straight toward the rear of the car where we want them to be seen. Install them into a slanted fender surface and they will not be visible very far behind the car.

The third issue with LED's is this - by nature they are a single function light, either on or off. In order to use them as a taillight that needs two functions (taillight plus brake light/turn signal) we must have two different groups of LED's to do the two different functions - or - we have to trick a single group of LED's into doing both functions by using a little devise called a converter. Nothing more than a small group of electronic components, the converter steps down the volt­age to the LED's slightly for the taillights, and gives full voltage for the brake/turn signals. It also keeps those two circuits from cross-talking to each other. Cool stuff!

Finally, the small amperage drawn by LED's may not "drive" a regular automotive flasher used for the turn signals. "Can" flashers work by having amperage warm an internal bimetallic strip. The strip heats up and breaks the circuit, cools down and completes the circuit. This happens about 90 times a minute to give the flashing effect. To solve this problem you need either (1) extra current draw provided by keeping bulbs for the front end or resis­tors called dummy loads (think of them as extra lights that don't light up), or (2) a special "no-load" flasher that will work with LED's.

Will incandescents and LED's work together?
Yes, but maybe not -sounds like a stupid answer, but let me explain. If an LED light is properly made, it is just one more component in the electrical system and will work perfectly in conjunction with incandescent bulbs. However, there are LED lights on the market that work only as a complete system, only with LED lights and only with lights from the same manufacturer. That is fine if that is what you want for your car. But what if you want to keep the bulbs in the front of the car and just add LED taillights? Then those "system" lights are not for you. They force you to use only that brand of light and prevent combining lights to get the effect you are after. Be sure to ask before you buy to make sure that what you are getting will achieve your goals. At StreetWorks, all of our LED lights are made to work in combination with any other bulb or light.

In summary, when we make taillight modifications to our car or truck, we can use numerous combinations of lights and types of lights to achieve the look that we want. But we must be aware of the correct parts that are needed with each of those combinations to achieve the taillight functionality that we need. If LED's are part of our plans, understanding the characteristics of LED lights will help assure that you take full advantage of their unique benefits and end up with neat, bright taillights for your ride. Enjoy!
 

(c) Watson's StreetWorks, LLC 2001

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