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Check that the polarity on your power is correct.
Also make sure that a voltmeter set on AC does not detect considerable AC on the power line. That can happen, and devices don't like it.
That voltage may not be adequate. 13.8 V is the rated voltage mentioned in the spec.s for this device (if the 535 you have is made by Garmin, that is. I am assuming so.) You may need at least a volt more of power, since undervoltaging is as disliked as overvoltaging, oddly enough.