No, that is a fuse for your batteries. There is a compartment known as THE BCC, battery control center on the front engine fire wall. About 6 x 8 x3" black box. Open the door and you will see a reset button, push it. It is another fuse to protect your motorhome.
It cuts all 12v circuits. The reason you get power when plugged in to shore power is it is coming from your iconverter. The transfer switch is not relative to 12v. It's purpose is to isolate the 120v AC sources you have available to you, shore AC and generator AC. If you have 12v DC when plugged in to shore power then the transfer switch is working. And the converter is working.
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