Change tail light led's

The resistors may be the problem, but because I can't see the rear of the circuit in the photo, I can't really give any specific advice. The proper value of the resistor depends on how the leds and resistors are wired together and how many are in each group.

I assume that since you decided to attempt this project that you already have knowledge of electronics. I hope you don't take my comments as condescending or an assumption that you don't know these things already, I'm just offering the information to help in case you don't already know it, or if you do already know, maybe it will encourage you to recheck something that will hopefully lead to the resolution of the problem.

The most common reasons an LED will fail to illuminate:

Incorrect Polarity: unlike a light bulb, the led must be installed with a specific orientation with respect to the positive and negative sides of the circuit, or it will not work. Have you checked to be sure you used the proper polarity? An led can be damaged and fail if installed reversed. If wired in series, any leds following the reversed led in the series will not work -that is to say if the first in the series is reversed, none will work.

Improper Power Supply: Did you verify that the supply voltage was present and correct? If a resistor with too low an impedance is used for the given circuit, the LED can be destroyed in an instant. Since the old resistors are of a higher value than those supplied with the new, hopefully this scenario is unlikely. As was said by a previous poster, it is possible that the resistance of the original resistors in the unit is too great and is preventing enough current from flowing across the new led for it to work. I suggest bench testing the new leds outside the light fixture with just some resistors and a power source. Once you've verified correct operation and a proper resistor value, then the next step would be to inspect the circuit of the light fixture and determine what what changes to the resistors will achieve the correct resistance in the circuit.

Damaged During Installation: A surface mount type led is sensitive to the heat of soldering and can be damaged during installation. It is important to not use too high wattage of a soldering iron and also to use care to work quickly and carefully while soldering to avoid excessive heat build up in the led.

Could you tell us more about what you've done so far in the project? What troubleshooting steps have you tried so far? Have you already exchanged all the old leds for new on the light fixture? Are the traces visible on the rear of that circuit board?

I'm happy to hear you sorted it out!

To correct the flashing speed the most common method used is this:

A resistor is connected between the positive and negative power supply wires to each LED fixture. What I mean specifically is that if you were to do this fix yourself, you would strip back a bit of insulation on the positive and negative wires leading into the tail light and solder one side of a resistor to the positive wire and the other side to the negative. The theory is to put the LED into a parallel circuit.

The correct value for the resistor depends on a number of variables and it will likely take some trial and error to get it just right. Obviously, the left and right fixtures should probably use the same impedance resistor in order to have a balanced flash speed. The impedance will likely fall somewhere between 3 and 8 ohms -so there's a starting point. Select a 20 watt or up resistor to be safe -a normal 1/4 watt won't do here. The resistor will build up some heat, so I suggest a heat sink, or using some heat sink compound and sticking it to the metal chassis of the car somewhere to dissipate the heat.