Faulty LED

[Howard Wright]

Hi All

I’ve had a most frustrating afternoon.  

I mentioned in another post that the brake light switch on the Brookfields was sticking on.  What I hadn’t realised that when pressing the brake pedal both the brake and side lights came on!  I only realised as the front sidelights came on as well. The sticking switch was easily solved the brake and sidelight situation not so.

I know you shouldn’t assume anything but my wiring was, to me, the obvious culprit.  A couple of hours later and the wiring checked and rechecked the real problem turned out to be a faulty LED bulb.  The stop tail light was bought from a good supplier (I can’t remember which one!) and has worked OK for two years!

So if you have lighting gremlins don’t immediately jump to conclusions and bulbs can turn faulty!

Cheers

Howard

[John Cornforth]

Hi

I know I have mentioned this before, but some LED Stop+Tail bubs are actually just a single LED with two different values of feed resistor. This gives high/low current (and therefore brightness) depending on which one is connected to a live supply.

This generally works OK, but with some setups there is the risk of current going the "wrong" way back out of the unfed resistor, which then enters another lighting circuit.

The cure is to use small series diodes, but it's a pity they aren't built in as standard.

[RenaudR]

A diode would indeed prevent the current going back but it goes back because the earth is bad on this bulb. Better fix the wrong earth then no back current and the bulb works!

[Denis Sweeney]

Not sure who’s LED’s you are using and am no expert on anything electrical, but looking at Dynamoregulatorconversions website, which has a lot of notes on the use of LED’s, the main problem they highlight for failures of lighting systems with LED’s is poor earthing.

[Howard Wright]

Hi All

Thanks John, good explanation.  I can definitely say that the earth was good. I wire an earth lead to all lights etc.  if it was an earth problem switching bulbs would not have cured it!

Cheers

Howard

[Parazine]

the main problem they highlight for failures of lighting systems with LED’s is poor earthing.

I concur, the only time I have had LED failures, the cause turned out to be a loose earth lead on the battery. It also affected the starter motor....

[Duncan Grimmond]

On the five various cars I've built over the last 20 years I've always gone to the same auto sparks pal who installs a separate earth wire to each item rather than relying on a common earth through chassis/bodywork. I've never had an earth problem so far, touchwood!
(Perhaps I should not have said that...)

[David Cochrane]

All Austin 7 wiring should use a wired earth return. Never rely on earthing via bodywork. Fitting earth wires is the simplest way of improving lighting, starting, etc, and it should be one of the first things to do to your car.

[andrew34ruby]

All Austin 7 wiring should use a wired earth return. Never rely on earthing via bodywork. Fitting earth wires is the simplest way of improving lighting, starting, etc, and it should be one of the first things to do to your car.

So Herbert did it all wrong then? And I've done it all wrong again? All cars on the roads, then and today, use the body as an earth return. If done properly there is no problem in my experience.

[Duncan Grimmond]

Earthing to body/chassis is almost invariably the cause of the often seen "miss flash" through brake or tail lights to the "miss brake" light through the indicator commonly seen on cars over 8 or 10 years old. Body to chassis electrical continuity is fine on a new vehicle until perhaps the guarantee runs out after which the manufacturer has no care or responsibility.
An added earth on a new or 80 year-old vehicle is a perfect(ish) example of fit and forget.