Toyota Repair: Toyota blinker all blink fast, gm cars, flasher relay

Question
This is related to the other question I searched for and found some good info on.  The only difference is that all of the bulbs work on this 98 Camry.  The blinkers work fine and flash slowly until the headlights or brakes are pressed, then they blink fast, and all of them work.  I was told the dealer installed brighter headlights, but even with those bulbs removed the blinkers flash fast when the brake pedal is depressed.  Rear bulbs match the P/N in the owners manual.  The car may come back in a few days for further diagnosis.  I suggested replacing the headlights to OEM and trying a blinker relay for S&G before go for the blinker switch since that cost is highest.  Most of my experience is with GM cars.

What would you check next?

Answer
The headlights won't cause this, the most likely cause may be the flasher relay since all turn signals are affected. Make absolutely sure that none of the bulbs in the rear are good and installed in the correct sockets and the ground connections are good.