Like some owners
, don't the spark boxes normally produce a whining sound when switched ON? If so and they don't, you may want to look for a system fuse or other common (or independent) source wire, then diagnose with your multimeter to see where the voltage doesn't continue.
It's not common for devices to fail at the same time although it could happen. I'd look outside of the spark boxes if both exhibit the same symptoms; common ground wire, signal wire, harness connector, malfunctioning ignition switch?
Sherwood