My fault! I swapped the direction of the diode and screwed up the wiring. I hope the coil voltage level is because R3’s value is too low, I increased it to 470K which will need much less current to change the voltage and hopefully increase the voltage from the coil enough to trigger the 555. The input shouldn’t need very much current but it does need to get down to about 1/3 of 12v to trigger I think. If that doesn’t work we may need to add another resistor to ground from the trigger pin to get the DC bias closer to the trigger level so the pulse from the coil will trigger the 555. The idea of the two diodes is D2 will only let the input get to 12.6v at the trigger pin if the coil generated more than +12V and D1will only let the voltage at the trigger get to -0.6v if the coil gets below ground, they may not be needed if the coil doesn’t generate that much voltage. This sketch should be correct I think (or at least hope 
). If this doesn’t trigger, please measure the voltage swing the coil produces at pin 2 of the 555 and I’ll try and figure out a resistor value that will let us trigger on what we get by biasing the trigger pin closer to the threshold. I’ve added (but not finished connecting) R4 in this sketch in case we need to try the dc bias trick.
Timing_light_new3.fzz (13.2 KB)
Peter