I've run into this before with mechanical flashers with a mix of leds and regular bulbs. The power resistors are usually total shite and don't balance the load for crap. The power resistor is making the mechanical blinker happy but not the led. Just a guess

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Matthew Vogt
96 Mazda B4000
4.0 4x4

If the women don't find you handsome, they should at least find you handy