LED turn signals blinking fast: what the flasher relay does

After swapping bulbs for LEDs, turn signals often start flashing twice as fast. It is not a fault: a stock relay senses current, and LEDs draw far less of it.

• Make sure every LED is working and the contacts are clean: one dead lamp also causes fast flashing.
• Identify the stock relay type: two-pin (current-sensing) or three-pin (electronic). The connector or the owner's manual will tell you.
• The cleanest fix is an LED-compatible relay of the same type and pinout.
• The alternative is load resistors wired in parallel with the lamp. They get very hot, so mount them on bare metal, away from plastic and wiring.
• After installing, check the flashing from all sides, including the hazards. The rate should be steady, roughly 60 to 120 flashes per minute.