Need a little alt. help

[cleanfreak]

I have a 68 with gauges , previous owner installed a 10si , leaving the voltage reg hooked up. This worked a surprisingly long time (1 year) , alternator quit charging. I eliminated regulator , Is the brown wire at regulator supposed to have voltage with key on? What I have found this is supposed to be the "excite" wire for the 12si , but it has no 12v sig. If so , where does it pick up 12v , as my truck doesn't have a gen light (that I can find). Any help is appreciated - Bob