Be sure to set the includedefaultsources to false
var searchWidget = new Search({
view: view,
allPlaceholder: "Search by street address",
autoSelect: true,
suggestionsEnabled: true,
includeDefaultSources: false,
sources: [
{
locator: new Locator({
//url: "https://geocode.arcgis.com/arcgis/rest/services/World/GeocodeServer" //World GeocodeServer
url: "your GeocodeServer"
}),
name: "City Locator",
placeholder: "Street Address",
zoomScale: 1000
},
]
})