LED Stop and Tail Lights
Why they flicker when other circuits are powered.

Indicators: The line at A represents zero volts and the line at B represents 12 volts on the green circuit i.e. fused ignition. The trace starts the instant power is applied to the indicators, showing a reduction in the supply voltage throughout the car of about 3 volts for about 5 milli seconds while the incandescent filaments are heating up.

  Fuel pump: Again the line at A represents zero volts and the upper line is the system voltage when the fuel pump is energised (point B) and de-energised (point C) i.e. one click. The reduction is system voltage is much briefer, but also much deeper dropping by more than half. The difference between the upper line either side of C represents the 'steady state' reduction in system voltage while the pump solenoid is energised, and is about half a volt, for the six amp load.