With electricity, you follow the flow.
1. be sure you have current TO the converter (if no, breaker/connection)
2. be sure you have current AT the converter input (if no, wire/connection)
3. be sure you have current AT the converter output (if no, converter/fuse/connection)
4. be sure you have current at the battery. (if no, fuse/wire/connection)
When you find the first spot in that list without current, you have drastically narrowed down the list of possibilities, and should know where to look further.