The PlusX, Plus III, and Plus IV have well-designed triggering circuits that can safely handle a wide range of sync voltages and compatibility. They expect flash packs to have their sync circuits wired in the correct industry-standard polarity, however. Sometimes flash packs are not wired in the correct polarity. This simple adapter corrects that!Connect this adapter to your Plus radio, then connect your sync cable to the adapter. Compatible with all PocketWizard Flash Sync Cables.Reversed Polarity Symptoms:You may have a polarity issue if any one of these are true: When you connect the flash to your Plus radio, the LED on the Plus turns red and stays red, like it is stuck transmitting all the time Your flash fires once, but then never again With the sync cable already connected to your Plus, connect the sync cable to your flash. If the flash fires as you insert the plug, that is a reversed polarity symptom