The Arduino interface board is usually wired up with a common ground with switching perform on the outputs (+5 VDC).
When working with OEM equipment this arrangement can be the opposite – korries on the panels are wired up with a common anode (+5 VDC), and switching performed with ground.
With incandescent bulbs this does not seem much of an issue as current can be supplied bidirectionally; however with LEDs current must flow in a single direction for functionality. The incandescent bulbs in the korry of several panels have been swapped out for LEDs.
All is not in despair – fortunately the Arduino boards provide a 5 VDC+ output which you can connect the common anode. Connect the GND wires to to be switched to the outputs. When setting up the avionics interface ensure you assign the output to be reversed. If you are using Arduino737 software to interface with ProSim, select “Output REV” for the given terminal.
The korries should now light up appropriately and correctly as assigned with common anode wiring.
Soarbywire 
Dont you mean common Anode if all the positive sides are tied together??
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The LEDs are common cathode in the korries (common ground), but the wiring in the cannon plug it self is common anode (if that makes sense).
I have changed around cathode to anode on the article – there was a bit of confusion. Cheers.
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