I have a 89 g30 w/ 454, don't know if they have the same alt. I wasted my time following the brown wire back to the fuse block, no connection. It's for people who have an idiot light. The newer alt with a gauge is uses 2 wires. The charge wire, the biggest red one and a pink/ black stripe to turn it on. If you check for power at each wire you should have battery voltage, no drop. So if your battery is dead @ 8 volts you should see 8 volts @ each wire. If you have nothing on the pink/black check all the red wires that go into the fuse block, you should have full batt. voltage. If not follow that wire back to the fusible link and check the link. If no voltage to the largest red charge wire follow it back and do the same. Remember you still have to clear the fault, so buy at least 2 links if you replace any of them, the new one may blow until you find the fault. You said you changed the fuse for the gauges so you probably blew a link, also check all the fuses in the block as other fuses on the block branch off and protect other smaller fuses on the same block.
Note! I have a CS style alt, with a 4 pin plug that only has 3 wires coming off the plug. Be carefull with the wires on the plug, they are small and frail and will break inside and you may lose the connection at the plug if you pull it by the wires.