A little modern technology can be good for old cars, but you've got to know how to integrate and use it properly. That's a lesson we learned recently when we replaced the standard-issue 1157 taillight bulbs on one of our rides with new-fangled LED-or Light Emitting Diode-bulbs. With LEDs, we reasoned, we'd get brighter, longer-lasting taillights without the heat of high-intensity bulbs. Several benefits in one-how could we lose?
Everything was going fine until we got the LEDs installed and went to test the turn signals in the driveway. Nothing-no blinking, no flashing, no nothin'. Perplexed, we retraced our steps, double-checked our connections, and tried it again. Still nothing. Time to call in the experts.
Standard bulbs vs. LedsOur quest led us to Greg Schlup at Hotronics, who sat us down for a little lesson. It seems our problem was a common one rooted in the difference between incandescent light bulbs and LEDs.
Incandescent light bulbs generate light with a filament-actually two of them in an 1157 bulb (one for the taillight, another for the brake light). Light is generated when electricity flows across and heats up the tungsten filament. By contrast, LEDs have no filament. They produce an electrical arc that jumps across a gap. A reflector behind the arc directs and focuses the light, which is what we see glow.
In addition to operating on different principles, LEDs are much more efficient than incandescent bulbs. They're so efficient, in fact, that they don't draw enough amperage to activate the typical metal canister automotive flashers. That explained the sudden lack of blinkers on our car.
The FlashAs part of our lesson, Schlup explained flasher fundamentals, too. Standard automotive flashers, such as the 552-type used on many cars, work in a similar fashion to the old mechanical voltage regulators from the '50s and '60s. When you activate the turn signal, electricity flows through the flasher across a thin bimetallic strip. As the strip heats up, it bends away from its contact, cutting off the electric flow and making the lights blink off. The strip then cools off and makes contact again, completing the circuit that turns the lights on, and the process begins anew. It's repeated dozens of times per minute, providing the blinking lights we use to signal turns.
Standard flasher function requires a certain amount of electrical load to properly heat that metallic strip. LED lights, however, require so few amps that the electrical load typically won't activate a normal flasher. There's a chance it'll still work if you keep incandescent bulbs in your front turn signals and only use LEDs in back, but if there are LEDs at all four corners, forget it.
Rodders have come up with several solutions for making LEDs function as flashers. One is to wire in a load-equalizing-type shorting resistor, a method Schlup does not recommend, likening it to connecting jumper cables to a battery and touching the other ends together. Such resistors, Schlup says, "short circuit the electrical system, drag the voltage low, create extreme amounts of heat, and have set fires and melted wiring."
A better option, Schlup says, is to use a no-load flasher such as the PG-3 unit sold by his company. Unlike traditional flashers, the PG-3 is a solid-state, 100-percent electronic device that has a built-in relay for switching independent loads. It only needs a very small electrical load to recognize a complete circuit and start the flashing process. Thus, it can be activated with something as small as an incandescent dash indicator bulb or small motorcycle signal lights like those many rodders use on the fronts of their cars. Once it's on, the unit's internal relay pumps out 5 amps at full system voltage to the LEDs and carries current through the front, rear, and dash bulb directional circuits. In other words, your LED lights get full system voltage, so they're as bright as possible.
This sounded like a simple enough solution to us, but we wondered what we'd do if every turn light in our system-including the front signals and dash indicators-was an LED. Schlup had an answer for that, too: use relays to trigger the PG-3. A relay can be wired into each rear signal circuit and the no-load flasher will sense the electrical path has been completed through the relay coil. A chart supplied with each PG-3 shows how to properly wire the relays. Furthermore, by using the small relay coil as the established electrical path, even higher amperage loads can safely be carried to the rear signal lights-enough current to power multiple LED cards or trailer lighting if needed.
For the most part, installing the Hotronics flasher is a simple matter of removing the old 552 canister and plugging in the PG-3, as it's built with the same two-prong design. The biggest difference is that the PG-3 has a ground wire that needs to be connected to a clean body ground.
There's one possible catch, though. Schlup has learned that many aftermarket wiring harnesses have the flasher sockets wired in reverse. If you look closely at a 552-style flasher, you'll see a small "X" and "L" stamped near each terminal. The "X" indicates 12 volts in, and the "L" is the load to the lights. The PG-3 is designed similarly-12-volts in is marked "IN," and the "OUT" terminal indicates the load to the lights.
Standard flashers aren't picky-they'll work in reverse since the bimetal contact strip heats up regardless of which way the electricity flows. The PG-3, on the other hand, requires current to flow in a specific direction since it's a fully electronic device (your radio won't work when it's wired backwards-the PG-3 reacts the same way). Chances are everything will work fine if you're plugging the no-load flasher into an OEM harness. If you've got an aftermarket harness, you may want to get out your test light, turn on the ignition, and determine which side of the socket is "hot." If this does not correspond to the PG-3's "IN" terminal, you'll need to reverse the wires in the flasher socket or make two small jumper wires to hook it up properly.
Light It UpWe're not sure about you, but we never realized there was so much to know about bulbs and flashers! We hope we've shed a little light on the subject here. After all, taillights and blinkers are nothing to take lightly-they're the only things standing between your car and the one behind it.
More Led FactsWhile LED lights have benefits like bright light and low heat, they also have their quirks and limitations. Here are a few facts you should know.
LED light is not white, or at least we're unaware of any company making LED lights that shine white. Most LEDs in the street rod market generate a red, orange, yellow, blue, or green glow.
Each LED is generally very small, so they are bundled together for maximum effect. For instance, the 1157-replacement LED shown in this story is actually a grouping of 15 LEDs.
LEDs have a narrow viewing angle. Whereas regular bulbs scatter light in all directions, each LED element typically has only a 20- or 30-degree spread of light. As a result, they look bright when you're directly behind them but lose their glow at an angle. When used for taillights or brake lights, make sure LEDs point straight toward the rear of the car, not on an angle.
"Bulb-style" LEDs, like our 1157 replacement, throw out a very focused beam of light. They will usually work well on small taillights but may only light up a small portion of larger lenses.
As an alternative to "bulb-style" lights, LED cards are available in the same shape as popular street rod lenses ('39 Ford, '50 Pontiac, etc.) and are designed to distribute light more effectively. Some aftermarket taillights, like the Chevy-style lights from Southern Rods & Parts shown here, combine the LED card and lens in one piece.
