I have swapped my boot lights in the car for these Led cob lights 

 

The original light fittings as they were have a tiny (resistor (I assume) and I have wired the led's before the resistor therefore bypassing it.

The lights are working fine at the moment without the resistors in the circuit. 

 

Should i have used the resistors and what would be the purpose of them in the original lights???

The original bulb would be 5 watts each side i believe, and the Led's read about 4 watts each.

 

Cheers

For DC LEDS, the resistor is to drop the supply volts to that needed by the LED. A LED has a forward volt drop of a certain voltage at a known current. For DC working , the resistor is  calculated using the formula 

R= (SUPPLY -FORWARD VOLT DROP) /CURRENT (IN AMPS). ( R= resistance in ohms ).

The idea is to limit the current through th LED.

 

The original lights would have had a blocking diode, so they only work when wired in the correct way

 

A normal bulb would work either way the polarity went

10 hours ago, VWD said:

For DC LEDS, the resistor is to drop the supply volts to that needed by the LED. A LED has a forward volt drop of a certain voltage at a known current. For DC working , the resistor is  calculated using the formula 

R= (SUPPLY -FORWARD VOLT DROP) /CURRENT (IN AMPS). ( R= resistance in ohms ).

The idea is to limit the current through th LED.

That's often only part of the story for car LEDs though - as you correctly say LEDs have a forward voltage much lower than the 12V (nominal) of a car electrical system (somewhere between 2V and 5V depending on the LED colour), but many car LEDs also have a resistor in parallel (not with just the LED but with the series combination of LED and current limiting resistor) to 'fool' older bulb failure warning systems by drawing enough current to make the system think a normal incandescent bulb is still fitted.

I should have said the original bulbs were normal bulbs (before i removed them) so i'm not understanding the blocking diode bit.

 

And the boot lights would not be a part of the canbus system afaik.

 

I know there is a positive and a negative on an led.

 

They measured 4 watts when powered using a 12volt constant voltage led driver though not sure if a constant current driver would make any difference or be preferable for this purpose.

Blocking diode is also referred to as a safety diode. LED and other semi conductors don't like reverse volts. So to stop this some better manufacturers ( and almost all amateurs) will wire a diode in series with a circuit to prevent "finger  problems". Dead easy to reverse wire a circuit and then you thank yourself for  wiring in a safety diode. In essence a diode conducts only in one direction. So wire one in series with the internals of a circuit( to allow current flow in the correct direction)  and you've built in protection. No chance of expensive smoke when a semi conductor gets a +ve up the negative side.

your circuit looks like it needs some sort of voltage regulation on the lines. Simplest way I've found is to find a way of dropping the car volts to a lower voltage and then using an inverter chip ( of correct wattage) to provide 12v at the required current. However, if the boot lights would only be used when the car is stopped ,with engine off, then it becomes simpler. I'd suspect that the battery volts with engine off would be circa 12-13v. No need for circuits to regulate the supply to the LED.