OOh! A bit more complex than that. I've seen cars where LED sidelights or number-plate illuminators have been fitted, and they've blown or gone faulty within weeks.

Whilst LEDs seem to work for ever with a steady DC battery supply, when fitted to a vehicle, where voltage tends to spike a bit when the vehicle is started or revved, LEDs just don't seem to survive for any time!

On a vehicle, LEDs need a Driver circuit. A recent 'Top-Gear' show finished with Jerremy Clarkson in front of a modern car with LED front 'running' lights. These LED lights appeared to be flashing like indicators on the TV, even though they would have appeared to the studio audience as being steady. That was because the LED lights had a driver circuit which pulsed the lights, and the 'strobe' effect between the pulsing of the LEDs and the frame rate of the video gave the effect that the TV showed the lights as flashing.

LEDs used for traffic lights - the little Green Man and Red Man lights for the pedestrian phase - they're pulsed with a driver circuit, too. Just look at one at night when you stop at the lights. Twist your head from side to side and you'll see a line of green or red men!

As for the supplied resistors, they are to give the required load for the indicators. Side-lights don't matter. When side-lights are switched on, it matters not a jot whether you've got two at 5 Watts each, giving a load of 10W, or two at the front and two at the back, giving a load of 20W, or if you replace them with lower-power LEDs - they'll still light up.

But the indicators have a little unit which switches them on and off at a given rate. If a bulb fails, the indicator will click at a much faster rate, and the one working bulb will flash at that faster rate. Take out the two 5W incandescent bulbs and replace them with low-wattage LEDs and the indicator unit just won't work properly! So the resistors are to be fitted into the indicator circuits in order to give the required 5W per bulb so that the indicators flash at the correct rate.