If you use them for indicator bulbs you need to do one of two possible modifications because the LED bulbs only draw a small current which isn't enough to operate a standard bi-metal strip flasher unit.
Either
1. Wire a ballast resistor in PARALLEL with each of the 4 indicator bulbs to increase the current draw.
Or
2. Fit an electronic flasher unit which operates at the correct rate regardless of the amount of current flowing in the circuit. This would be the better option and, if you fit a high power electronic flasher unit it will work with LEDs, filament bulbs or a combination of both.