I have discovered that the standard running lights (7443 bulbs) on this vehicle do not seem to be compatible with the newer 7443 LEDs. I've tried two different brands and both of them do not function as day time running lights. They only turn on when the head lights are turned on.

I talked to my local mechanic, the Fiat Dealer (parts department, I got "duh"), and another forum I am active in and no one knows why the LEDs don't work. IF I was to guess, I'd say it's a voltage issue, not enough in the daytime running light mode, for them to come on, but I have not tested this theory with a volt meter.

Anyone know the answer?
Anyone know if there is a brand of 7443 LEDS that would function as daytime running lights on this vehicle?
THANKS!

Can't directly answer your question/problem but:

Normal incandescent daytime running lights are designed (by regulation requirements) to be bright when the headlamps are off and then must dim when the headlamps are on.

There are a number of reasons for this, one of the main ones being that for LED DRLs then at night they would be too intense and omni radiant causing spots etc. to a fully open iris in otherwise dark conditions. Similar effect that a low powered laser beam can be readily seen and do eye damage but has little illumination capability.

Now this is rather reverse to what you are experiencing in that during the day DRLs should be getting the full 12V and night/headlamps on only getting 6V or 9V.

On modern cars then dropper resistors are not used and the 12V supply is pulse width modulated (50% on / 50% off or 60% on / 40% off). This works extremely well with filament bulbs but it often an issue with LEDs. This is why some LEDs are marked as suitable for dimming control whilst others are not.

Your situation I found in a Lumie bedside lamp/radio/clock

Lumie Bodyclock Starter 30 Wake-up Light Alarm Clock - The Original Dawn Simulator: Amazon.co.uk: Health & Personal Care

I replaced the filament bulb with a dimmable LED and the brightness would step from 0 to 10 to 20 to .... 80% to 90% but at so called 100% LED dimmed back to a lower %. So what you are experiencing is similar to what I found with the Lumie light.

s130 said:

Can't directly answer your question/problem but:

Normal incandescent daytime running lights are designed (by regulation requirements) to be bright when the headlamps are off and then must dim when the headlamps are on.

There are a number of reasons for this, one of the main ones being that for LED DRLs then at night they would be too intense and omni radiant causing spots etc. to a fully open iris in otherwise dark conditions. Similar effect that a low powered laser beam can be readily seen and do eye damage but has little illumination capability.

Now this is rather reverse to what you are experiencing in that during the day DRLs should be getting the full 12V and night/headlamps on only getting 6V or 9V.

On modern cars then dropper resistors are not used and the 12V supply is pulse width modulated (50% on / 50% off or 60% on / 40% off). This works extremely well with filament bulbs but it often an issue with LEDs. This is why some LEDs are marked as suitable for dimming control whilst others are not.

Your situation I found in a Lumie bedside lamp/radio/clock

Lumie Bodyclock Starter 30 Wake-up Light Alarm Clock - The Original Dawn Simulator: Amazon.co.uk: Health & Personal

I replaced the filament bulb with a dimmable LED and the brightness would step from 0 to 10 to 20 to .... 80% to 90% but at so called 100% LED dimmed back to a lower %. So what you are experiencing is similar to what I found with the Lumie light.

Click to expand...

Thanks for the reply! This is what I was thinking a variable voltage issue, which If I understand what you are saying, means the LEDs I've tried run on the lower voltage (with headlights on), but don't work on the higher voltage they would be getting in daylight running mode, with the Headlights turned off.

So the question becomes, is there a 7443 compatible LED dimmable light bulb that would work in my car as a daytime running light?

Well if I were you I would try your LED bulbs in say the rear side light or brake light positions. Unless your 2012 500 is like the 2015+ 500X which has two bulbs that are used in parallel for side lights and brake lights (side = both dimmed, brake = both full) then you can test you LEDs in a stand full 12V supply that is not modulated. Or you could use a 12V battery to test the full 12DC functioning.

From an electronics points of view many "pulse width modulated" circuits can go from 0% to 99.xx% but not 100%. This is because their algorithm is ON .... OFF followed by ON ....OFF or just OFF. They do not have an ON .... ON followed by an ON .... ON cycle.

It could be that the window between 99.xx% and 100% is fooling the LEDs own regulation circuits. Remember that LEDs are constant current nominal 1.2V devices so can not take a full 12V. Stringing 10 LEDs in series would work but when the alternator kicks out 14.xx volts then the LEDs can see uncontrolled increases in current and thus reduced life. This is why you will see all those little electronic chips on circuit boards in all LED bulbs.

LEDs require a fixed voltage to work. They dim by lowering the current that passes through them. Incandescent DRL circuits work by reducing voltage. Neither bulb will work on a circuit designed for the other.

Garrett500 said:

LEDs require a fixed voltage to work. They dim by lowering the current that passes through them. Incandescent DRL circuits work by reducing voltage. Neither bulb will work on a circuit designed for the other.

Click to expand...

Not quite true. LED diode emit light based on the current that passes through them. I'm talking about a single traditional LED diode. They are thus nominally constant voltage devices (called forward voltage at 1.2V minimum, to 2V for orange up to 3V or more for intense & blue). The actual forward voltage depends on the current passed through them but within reason the forward voltage is a nominal value.

The brightness of the LED is based on current. So to get a single LED to illuminate at 50% of rate brightness you would limit the current to 50% of rated maximum current. You could to this with the simple resistor off a 12V battery where at full brightness a resistor or R ohms is required and for half brightness a resistor of 2*R ohms is required.

As far as the visual brightness of an LED is concerned the the AVERAGE current must be lower than the maxium rated current. Resistors in series will do this but they waste power. Instead we can turn the LED ON at 100% brightness for a short period and then off for a similar period and repeat. Do this at once per second and we see a slow bliking light. Do it at 50Hz (50 times pers second) we see a flickering light, same many at 100Hz+.

Dimming any light by introducing a power losing resistor is not good design as though the light may be 50% lower the overall energy used is as iff the light had been on full brightness. It is the resistor that wastes the not require energy.

This is all about "switched mode power supplies and technology".

Modern LED based bulbs (collection of individual basic LED components) are actually driven and supplied by potentially complex switched mode regulation circuity. This is fine.

However these circuits can be confused/upset external modulations.

All depends on the final implements design in any one given LED replacement bulb.

Thanks all for your help. I have replaced my daytime running lights with the standard incandescent bulbs and they work.

I have a question about Headlights. I'm assuming my 2012 Fiat 500 has incandescent headlights. When the time comes is there an issue with swapping them out for LEDs?
Thanks.