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There is a 125 amp main fuse in the underhood fuse panel. This fuse is replaceable. If nothing is working, then this fuse is likely what is wrong. If some things are operational and others are not, then this is not going to be your problem. From the symptoms you are having, it sounds more like an ignition switch failure. It is fairly common for the ignition switch to go out on the Trailblazer.
so what is the part called? main fuse? relay?