I have looked at what is offered on various places on the internet for quite some time and I am not impressed with any of them. So, I am engineering some myself, but I am horribly slow. That means, don't wait for me, particularly since I am going to do city lights for a Golf first, anyway.
Things to be careful of are "high intensity" adertisements that are made with large numbers of 3 or 5 mm LEDs. They get their high intensity by focusing a beam, and will result in an overall shortfall in total lumen output while still costing quite a bit. In addition, if the LEDs are overdriven (usually the case) the life of the LED may be measured in tens of hours, rather than the thousands of hours quoted. After a relatively short period of time, the LEDs will begin to burn out and there will be a tremendous drop in light output.
My other problem with rear turn signals and lights has been the wonder of what will happen with turn signal function as well as a nosy computer that will try to figure out if the bulb is still there or not. Replacing a filament bulb with an LED will show the computer a higher resistance, so much so (in my case since a small 'feeler' pulse will be so small as to not be able to get through the current regulator circuitry I plan on using) that the computer would think the bulb is burned out and command the blinker to go into fast blink mode.
I just haven't decided what to do about it. Yes, I know about the parallel resistor 'fix' but I am trying to get around that as it is not esthetically pleasing to me.
Anyway, those are my thoughts for the moment, and I'll be happy to read anyone else's thoughts and solutions as well.
Cheers!