The 550 flashers were generally ok up to about 8 to 10 (or 12 if heavy duty) amps. I would be surprised if you added enough lights to total 8 or 10 amps but at the same time I can't say for certain. What is more likely is you may have a short somewhere. A dead short can kill a flasher right quick. Did you do some extra wiring to add those lights?

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end