Voltage present, even without fuse in DC distribution panel
The manual states that the panel has &quot;blown fuse indicators&quot; - red LEDs that will light when the fuse is blown.
The simplest way to do this is to connect an LED and current-limiting resistor in parallel with the fuse.  With a blown fuse (or no fuse) this would allow a small current to flow in the circuit - probably enough to light your test light dimly.