Watts = Volts * Amps. 300w = 120v x 2.5a = 12v x 25a. The cigarette lighter fuse should be 15 or 20 amp, so you definately could have been pushing the circuit's limits.
Judging from the symptoms, you probably fried a ground wire. One of the ground points, connector pins or wires could have been corroded - plugging in a heavy load pushed it over the edge. The higher than normal resistance across the ground point prevented it from carrying enough current to fry the fuse, so the corroded area just heated up (the dimming lights - a material's resistance increases with temperature, current flow drops as resistance increases) and nuked itself.
The dash light brightness controller, clock, rear defogger switch, cigarette lighter, gauges/indicator lights and speed sensor all ground through a single wire in the dash harness. The harness plugs into the dash fuse box which grounds the wire through G401 (driver's kickpanel) and G301 (driver's front corner of the engine bay). Have fun.
Judging from the symptoms, you probably fried a ground wire. One of the ground points, connector pins or wires could have been corroded - plugging in a heavy load pushed it over the edge. The higher than normal resistance across the ground point prevented it from carrying enough current to fry the fuse, so the corroded area just heated up (the dimming lights - a material's resistance increases with temperature, current flow drops as resistance increases) and nuked itself.
The dash light brightness controller, clock, rear defogger switch, cigarette lighter, gauges/indicator lights and speed sensor all ground through a single wire in the dash harness. The harness plugs into the dash fuse box which grounds the wire through G401 (driver's kickpanel) and G301 (driver's front corner of the engine bay). Have fun.
