Where is the voltage regulator?

[THE "10" SILVERADO]

Hey guys,
Been having some electrical problems lately. Headlights dim and get bright, volt meter jumping all over the place, and if it's related my thermostat is stuck on cold no matter what. Everything worked before the new engine. After reading around on here I'm thinking it's my voltage regulator. I have a 3 wire alternator so it's external, the only problem? I don't know where it's at. Does anyone know where the external voltage regulators are so I can replace it?

Thanks.