after 2 hours of troubleshooting one day (convincing myself the converter was bad) I found two fuses on the output of the converter. they were hidden behind the power cord.
Bottom line is there could be many reasons. Check the simple and obvious first (eg: battery cutoff switch, fuses, etc). Then break out the voltmeter. Always start at one end of the circuit and work towards the other. Don't start in the middle of the circuit. Either work from the battery to the lights, or the from the lights towards the battery.
Good luck (BTW - that i-con is two thumbs up!)