21st January 2018 

LED LIGHTS fitted to Classic cars can "create" unwanted problems.

The practice of replacing original filament type light bulbs for LED lights is becoming more common. If there is a safety or reliability benefit I see no reason why one should not. Simply taking out old bulbs and replacing them with LED units can create unexpected electrical problems for the following reasons.
1/Work is often done by owners who commonly believe they are simply replacing an old style bulb for a brighter modern bulb; this is not the case. You are changing a filament bulb which glows white hot for a diode which emits light.
2/The supplier of “said” LED replacement does not know the specific application that you intend to put there items too nor the exact electrical configuration, or polarity of your vehicle`s electrics.
3/In many cases the supplier of the LED light does not even quote the specification of their own bulb and I wonder if they themselves know.

LED stands for light emitting diode. The job of a “diode” is to control the flow of electricity both in amount and direction. In removing a light bulb and fitting a diode into your vehicle`s original electrical circuit you might well be creating all sorts of problems that you do not want (due to the properties of the diode).
For Example - a/ The flashing indicators might not flash – this may be because the indicator flasher unit requires more amperage than that which 2 LED units are drawing down (which is a very small amount compared with 2 conventional 21w bulbs ).
b/ The dash back lights no longer dim using the dimmer switch. This might be because the system was not designed for LED`s.
None of the new LED bulbs appear to work properly. That might be because of the polarity of your vehicle relative to the current flow for your LED`s is at odds.
c1/ The Battery charging warning light or ignition warning light (what ever you may call it) remains lit with the engine running.
c2/The battery upon my car no longer charges/ my battery is flat but everything else is fine. See below.
Below is a recent case history Jan 2017
I was asked to investigate several car charging systems all with similar problems. Simple issues, like my battery charges but the ignition warning light stays on or I have a bright ignition warning light but the battery keeps going flat. It appears that some owners have gone LED mad, buying entire set of LED`s for every bulb upon their vehicle from Ebay or similar. In replacing their ignition warning light with a light emitting DIODE, the electrical current that should be exciting the alternator into action, is virtually cut off. The resolve to both the charging system problems illustrated above was to remove the new LED and put back the original ignition warning light bulb. Some alternators will temporarily retain a magnetic memory. This enables them to produce power even though the warning light remains lit (be it the 2.5 amp or an LED). This is temporary and sooner rather than later, your alternator will stop working all together. By putting back the original bulbs a permanent resolve was created to both these cars problems.
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