The flasher is just a temp sensitive piece of metal across 2 contacts. As the current flows through the metal to the lights, it heats up, distorts, and the connection is broken. That cools it off and it comes back on again, over and over. If you add more lights(trailer, whatever)= more current so is just cycles faster. With too much current it may not flash at all or too quickly to see well. The heavier flashing unit just handles the current better so it heats up slower and will flash normally with a bigger load.

1997 T-100 4X4 Xcab,Warn Hubs
02 Camry LE
2008 Yaris