120v circuit works but the 12v circuit does not

I am guessing there is a fuse somewhere in the cable from the batteries, but I can not find it. Where should I look?
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If no fuse at battery, look at the fuse panel at the DC distribution panel
No 12v when plugged in either ??
Is the converter charging the battery when plugged in ?
Maybe the converter quit, and the batterys are dead. Its not like you gave much information.
Oh, the question, where's the fuse,...mayve there ain't one