What is a Diode?

["BDM" <bmims1@xxxx>]

My passenger door wiring has no power. I have removed the T-Panel on the top and cleaned the roof plugs. I have verified continuity from the roof plugs to the door harness wiring. I have verified the wiring continuity from the door light switch to the lights in the door. 

I have a wiring diagram and I suspect that the diode in the circuit is faulty. However, I do not know where it is located nor what it looks like. How do I check the diode and are the difficult to diagnose?

Any help greatly appreciated.

Bobby Mims
Tyler, Texas

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