MY MODIFICATION -- (Probably not the easiest way, but it works.) After some investigation, I realized that this little switch controls a lot. Other than just blinking the lights, it provides the logic for the brake lights. Therein lies the rub. Since I didn't have a 240Z turn signal switch I trusted (mine had been apart a lot, and the tabs holding it together were fatiguing), I used a 280Z turn signal switch I had handy.
Other than that, you'll need two 3PDT (triple pole, double throw) 12V coil relays. I used relays with 15Amp/240VAC rating contacts from SHRACK, model # 702012. You'll also need a +12v fused source which is high when the ignition is on.
(S1 is turn signal switch. I used a 280Z switch that was in good shape. A single pole of a good 240Z switch would work also.)
(a) The - - - - - - lines are lines of mechanical/magnetic connection through the three poles of each relay.
(b) The "arms" of the first and second poles from the right are both connected to the "G" or green wire. The third pole is connected to "GY" or Green-White stripe wire.
I mounted the relays together under the dash just to the left of the steering column, where the steering column bolts to the dash. This fix has been working fine for several years.