1) There is a circuit in the stock flasher that monitors load, and blinks faster if load drops. Normally it means burned out bulb. LED also consumes much less power than stock bulb, so it is detected as burned out bulb. There are two solutions:
- The right one: replace flasher with LED-compatible one. Something like that: http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&Page2Disp=%2Fspecs%2FEP27L.html
Not sure if it fits our vehicles, didn't do the research yet.
- The simple one: use load resistor 6 Ohm 50 watts. Here is the installation instructions: http://www.superbrightleds.com/pdfs/load_resistor_info.pdf
2) You cannot fix the brightness. Most of cheap LED bulbs are not bright at all. The problem is that their size is limited to the size of stock bulb. To produce a reasonable amount of light, LED bulb need to dissipate 5-7 watts of heat while keeping it's temperature below approximately 80C (176F). This is hard to achieve even with metal heatsink.