[VetteVet]

The brown wire usually comes from the resistance wire on the key switch accessory terminal on the gauge dashes and from the light on light dashes. It runs through the firewall to the external voltage regulator or in your case to the no.1 On the SI alternator. You should see 12 volts on the wire with the key on engine off and zero volts with the key off. If you are not getting that then your alternator is not charging.