What do you mean by "spiking"?
Since you have a Z4000, you should be able to get a rough indication of power consumed by the same smoke unit between engines. Watts = Volts x Current. The power should go up maybe 5 Watts for an SD24 from smoke OFF to smoke ON. Yes, the numbers on the Z4000 display will bounce around a bit but watch it for a few seconds and you'll get useful numbers. If you then transfer the smoke unit to another diesel it should consume the same power under similar conditions. This would test your hypothesis that the smoke drive electronics on the original board is the issue drawing too much power or delivering power to a phantom (unintended) load for whatever reason. If there's no smoke unit attached, the Z4000 indicated power should not change if you turn the smoke unit OFF and ON.
A diesel smoke unit at a given speed and output setting (low-med-high if using command) draws constant power. It should not be "spiking" unless there's an intermittent connection.
