PainlessPerformance 80111 Replacement Diode Assembly for Race Car Switch Panels

Will this stop my led fan switches from lighting up while driving and they are off?

What direction does the current flow?

Well this work for a alternator on the excite wire to stop the feed back

I have installed a headlights that came with 2 separated Diodes for each lamp, both are melted, how do I know the direction to install the new ones?