yes, please explane just how fast it is flashing. If all you are getting is a constant buz then you may have a cut wire somewhere.
The problem comes from too high a resistance, your lights are connected in paralel (two paths for the current to flow, one front, one rear) if one of those is cut, then the resistance doubles (only one path for the current) and the current halves (voltage = resistance*amperage).
what you can try is adding a third path for the current to flow by wiring in a potentiomiter (variable resistor with a knob on it), try using one that is around 10 ohms, you should be able to adjust the exact speed at witch the lights flash, however it may make your lights somewhat dimmer.
climb under your dash and look for a solid green wire (make suer it leads to the switch on the colum) and wire the pot betwine it and a ground (do NOT cut the green wire, just tap into it), then simply flip the switch on and turn the knob untill the desired effect is reached.
p.s., yes I am an EE