I can't imagine anything in the wiring or turn switch which would cause this. Normal behavior when not enough current is drawn by the bulbs. Usually due to a bulb filament being out, but can also result from using LED bulbs (draw much less current), as mentioned.

Cheap, basic flashers do this. I don't think it is intentional in the design, but can be thought of as a useful diagnostic. You can buy electronic flashers that have a constant flash rate, insensitive to current draw. Some will even play Elvis', "Love Me Tender" as you signal (quickly proved bothersome to me). You can also buy LED bulbs with a resistor to draw more current. Wasteful, but one way to keep using a cheap flasher w/ LED's.

__________________
1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans