Need to automatically switch a 12v 1amp dc pulse between 2 alternating outputs
Use a D-flipflop like the HEF4013 to switch between channels.



With each pulse the high level switches between \$Q\$ and \$\overline{Q}\$ and back. AND each output with the input pulse signal. Use the AND gates' outputs to drive MOSFETs like the FDC855. 

The HEF4013 is from the older CD4000 series, and normally I would suggest the 74HC74, but that one can't operate at 12 V. The HEF4013 can operate at a power supply voltage up to 15 V.

Don't forget the protection diodes across the solenoids.