As you already heard you have a short to ground. Disconnect the battery, replace or bypass the fuse. With the key on, take an Ohm meter (Batt powered Continuity Tester w/lt) and hook one side up to the fuse and the other to the chassis (Ground) You probably have 0 Ohms (Cont Light is on) confirming the short to ground. Start disconnecting various circuits/components. When the meter goes to full scale (Cont Light goes out) you have found the circuit/component that is shorted. Inspect this entire circuit carefully for bare wire, missing insulation, etc. Once repaired the Ohm meter reading between the fuse and chassis should be infinite (full scale) - Continuity Tester should not light.