If all the fuses are good, then maybe you have a loose connection at the converter, at a wall switch, or the main control panel if the lights switch there.
An easy way to check-- if there is a switch, is to pull the switch cover & switch out, then check the terminals of the switch with it in the "off" position. If the switch is getting current then it should read somewhere around 12-volts. You can also pull one of the non-working lights and check those (with any switches on) to see if there is voltage there. You can work your way out, checking voltage from the converter, to switches, and the lights, or start on the outside edge and work your way in from the lights. Working from the converter out is probably better... if there is a open connection near the end of the circuit then that may make it look like there is a problem closer in, too.
David & Elise
RAM 3500 SRW