Q: I just bought a cool Cadillac Fleetwood, and I’m upgrading it for day-to-day driving. One of the things I’m wondering about is if I can install LEDs in both the running lights and brakes.
A: Converting to LEDs has many potential advantages, including less draw on the electrical system, faster response time when you hit the brake pedal, and brighter brake lights. But the upsides may present an amusing problem: indicator signals. Many cars use a thermal flasher relay, which makes the indicator signals blink by using the applied current to heat up a bimetal strip that bends to open and close the circuit to the lightbulbs.
Because LEDs use much less current than a filament bulb, the light either won’t flash or will flash very slowly. There are several solutions to this.
With easy conversion in mind, there are aftermarket LED-lightbulb replacements with resistors that match the current draw to that of the original incandescent bulbs. You can also buy regular LED bulbs and replace the indicator signal relay with an electronic flasher that isn’t dependent on the bulb current. You can tell if a bulb is fitted with resistors if it’s advertised as “direct replacement” or if the wattage rating lines up with that of the stock incandescents. If not, it’s probably a resistor-free LED. Either way, you’re looking at R150 to R200 per bulb. It’s a worthy upgrade, considering safety is improved and you might never have to change bulbs again