LED lamps

I've been through a phase of bulbs blowing and decided to replace as many as possible with LEDs which have better resistance to vibration and a much longer life. OK, so they are believed to dim as they age, but a burnt out bulb is pretty dim too!

The speedo illumination lamps had both gone so that was the first job. I'd ordered a bunch of LEDs from Ultraleds in the 286 size, that is 5mm width push-in fitting.


For the back lighting I chose the wide 120 degree variant. This photo shows the silvered dead filament bulb and the slightly longer LED replacement. There seems to be plenty of space in the instrument unit for the slightly longer parts. I also swapped the neutral, lights on and high beam lamps.


Yes, they are a little bright, that could be a problem at night! I know that the turn indicator lamp could not be converted to a DC LED as current flows through the lamp in one direction for left turn and in the other for right turn.

Next up was the amber low fuel indicator. When I tested this by shorting across the float valve connector at the petcock the lamp only glowed dimly. The voltage was only 5V, but ramping up slowly. What was going on? Inspection of the the circuit diagram revealed a delay unit in series with the switch. This must act to smooth out the movement of the float valve when the petrol level is getting low. On replacing the bulb there was an 8 second delay between closing the contacts and the bulb illuminating. My main reason for fitting LEDs was for reliability, not current saving so I reasoned that I needed to draw more current through the delay circuit - just like when you fit LED turn lamps. I didn't want to add to the wiring so looked closely at the LEDs - they are just an LED, series resistor and reverse-current blocking diode stuffed into a piece of plastic.

So all that is needed is to fit an extra resistor inside the unit that will allow the delay to work. The bulb is a 1W item so passes about 83mA. There's no way that a 1W resistor will fit inside the LED case so I picked the lowest resistance that would not exceed 0.4W - the rating of the resistors in my electronics box. That gave me 330 ohms. It only passes 36mA, in addition to the 18mA drawn by the LED, but would that be enough? We'll have to see.




With a little care I was able to fit the extra resistor across the connections without it shorting. I squirted epoxy resin into the gaps between the wires and replaced it in the yellow housing. It protruded an extra mm but that's OK. It works, with a 15s delay which seems fine. In case you're interested, the delay component is a black box about 8mm x 15mm x 15mm just to the right of the airbox infront of the relay area. Only time will tell if this works.

Knowing that the LEDs are built like has 2 aspects. One, they may not be all that robust - the soldered joints are obviously hand done and are a weak point. Second, I can double up the construction to make an AC one for the turn indicator lamp; but not today.

The front sidelight had gone too. OK, so maybe it's pointless as the 55W lamp is on all the time, but perhaps, if the main bulb goes it would save a complaint by the Police? The bulb is close to the headlamp and Ultraleds warn that some LEDs will melt from heat. They do sell a metal bodied 1W item which is supposed to be heat resistant.

It has a large forward facing LED and gives off quite a lot of light. If you've disabled the headlamp this would be a worthwhile sidelight.

Whilst ordering LEDs I went for a red stop/tail light too. There are lots of these on the market, some with multiple LEDs, some that emit in all directions, some with white LEDs for the number plate. I elected to go for a single 3W rear facing unit.

This gives off a lot of light and must illuminate at least 120 degrees. I hoped the lens would give a good beam spread. I was pleasantly surprised at the beam pattern once installed. I had expected a very hot central spot with little to the sides, but actually, the facets on the lens spread the beam widely and the centre is not the most intense area.

It's hard to illustrate the distribution but this photo does show how much light is emitted to the sides. It's a lot brighter than the standard 21/5W item too. That should keep the cars away! Finally I swapped the dead number plate bulb, the frosted LEDs doesn't illuminate downwards much but is better than the nothing it replaced.