Explaining the circuit might help. With the key on, voltage must flow from the instrument cluster printed circuit through the volt lamp/resistor and back through the instrument cluster printed circuit, down the brown wire (ties into the cluster at the instrument cluster plug behind the instrument cluster) out to the engine bay and connecting to the back of the alternator (the brown wire ).
Troubleshooting: With the key on, check for bat voltage at the brown wire at the back of the alternator. Battery voltage must be present or the alternator will not charge.
If voltage is not present, pull the cover plate off of the instrument cluster and volt lamp and check for voltage on both sides of the volt lamp.
If you have voltage at both sides of the volt lamp, the brown wire has fried between the instrument cluster and alternator. You will have to pull the instrument cluster and pull the plug forward that mates with the instrument cluster, tie into the brown wire, and route the new wire to the alternator. Try a jumper wire first to see if you have found the problem before routing a new wire through the firewall. If you have found the problem, it can be a little bit tight splicing into the brown wire, but a new wire is necessary to fix the problem.