Originally Posted by Boharris
The fuse is BEFORE the dimmer knob. The fuse feeds the headlight/dimmer assy, the headlight/dimmer assy feeds the panel. The dimmer knob(rheostat) delivers the selected amount of voltage to the panel. In your case the fuse must be between your dimmer knob and the panel. Did you try this on your truck?
This is absolutely correct. Shoving a wire in with a blade fuse, you are sending 12V to that wire. Post dimmer switch is where I would go with RamTech's advice.
They also make blade fusees with a tab to put a wire with a spade connector on, instead of jamming it in with the fuse. That is some backyard mechanics that will bite you in the *ss sooner or later.