diff --git a/src/App/Components/Pages/MeterDetail.razor b/src/App/Components/Pages/MeterDetail.razor
index 1d00847..ec33cfa 100644
--- a/src/App/Components/Pages/MeterDetail.razor
+++ b/src/App/Components/Pages/MeterDetail.razor
@@ -214,20 +214,30 @@ else
             <MudText Typo="Typo.h6">@(_sourceEdit.Id == 0 ? "New source" : "Edit source")</MudText>
         </TitleContent>
         <DialogContent>
-            <MudSelect T="SourceType" @bind-Value="_sourceEdit.SourceType" Label="Source type" Class="mb-2">
+            <MudSelect T="SourceType" Value="_sourceEdit.SourceType" ValueChanged="OnSourceTypeChanged" Label="Source type" Class="mb-2">
                 @foreach (var type in Enum.GetValues<SourceType>())
                 {
                     <MudSelectItem T="SourceType" Value="type">@type</MudSelectItem>
                 }
             </MudSelect>
-            @if (_sourceEdit.SourceType is SourceType.HomeAssistant or SourceType.Mqtt or SourceType.Tasmota)
+            @if (RequiredEndpointType(_sourceEdit.SourceType) is { } needed)
             {
-                <MudSelect T="int?" @bind-Value="_sourceEdit.EndpointId" Label="Connector" Clearable="true" Class="mb-2">
-                    @foreach (var e in _endpoints)
-                    {
-                        <MudSelectItem T="int?" Value="@((int?)e.Id)">@e.Name (@e.Type)</MudSelectItem>
-                    }
-                </MudSelect>
+                if (ConnectorsFor(needed).Count == 0)
+                {
+                    <MudAlert Severity="Severity.Warning" Dense="true" Class="mb-2">
+                        No @needed connector yet — <MudLink Href="/admin/connectors">create one</MudLink>
+                        (set it up once; every source then just picks it).
+                    </MudAlert>
+                }
+                else
+                {
+                    <MudSelect T="int?" @bind-Value="_sourceEdit.EndpointId" Label="Connector" Required="true" Class="mb-2">
+                        @foreach (var e in ConnectorsFor(needed))
+                        {
+                            <MudSelectItem T="int?" Value="@((int?)e.Id)">@e.Name</MudSelectItem>
+                        }
+                    </MudSelect>
+                }
             }
             @if (_sourceEdit.SourceType == SourceType.HomeAssistant)
             {
@@ -305,6 +315,7 @@ else
         if (source is null)
         {
             _sourceEdit = new SourceEdit();
+            OnSourceTypeChanged(_sourceEdit.SourceType);
         }
         else
         {
@@ -332,6 +343,28 @@ else
 
     private async Task SaveSourceAsync()
     {
+        // A live source without a matching connector has no connection details and would silently
+        // never ingest, so refuse it here rather than letting it look configured.
+        if (RequiredEndpointType(_sourceEdit.SourceType) is { } needed)
+        {
+            var selected = _endpoints.FirstOrDefault(e => e.Id == _sourceEdit.EndpointId);
+            if (selected is null)
+            {
+                Snackbar.Add($"Pick a {needed} connector for this {_sourceEdit.SourceType} source.", Severity.Error);
+                return;
+            }
+
+            if (selected.Type != needed)
+            {
+                Snackbar.Add($"'{selected.Name}' is a {selected.Type} connector; a {_sourceEdit.SourceType} source needs {needed}.", Severity.Error);
+                return;
+            }
+        }
+        else
+        {
+            _sourceEdit.EndpointId = null;
+        }
+
         var config = new SourceConfig
         {
             EntityId = Trim(_sourceEdit.EntityId),
@@ -394,6 +427,44 @@ else
 
     private static string? Trim(string? value) => string.IsNullOrWhiteSpace(value) ? null : value.Trim();
 
+    /// <summary>
+    /// Which connector kind a source type needs, or null if it needs none (manual/import/virtual).
+    /// Tasmota has no endpoint kind of its own — it is served by an MQTT broker connector.
+    /// </summary>
+    private static EndpointType? RequiredEndpointType(SourceType sourceType) => sourceType switch
+    {
+        SourceType.HomeAssistant => EndpointType.HomeAssistant,
+        SourceType.Mqtt or SourceType.Tasmota => EndpointType.MqttBroker,
+        _ => null,
+    };
+
+    private List<IngestionEndpoint> ConnectorsFor(EndpointType type) =>
+        _endpoints.Where(e => e.Type == type).ToList();
+
+    // Changing the source type can invalidate the chosen connector (an HA connector cannot serve an
+    // MQTT source), so drop a selection that no longer fits rather than saving a mismatched pair.
+    private void OnSourceTypeChanged(SourceType sourceType)
+    {
+        _sourceEdit.SourceType = sourceType;
+
+        var needed = RequiredEndpointType(sourceType);
+        var selected = _endpoints.FirstOrDefault(e => e.Id == _sourceEdit.EndpointId);
+        if (needed is null || (selected is not null && selected.Type != needed))
+        {
+            _sourceEdit.EndpointId = null;
+        }
+
+        // Sole candidate: preselect it, so the common single-broker / single-HA setup is one click.
+        if (needed is not null && _sourceEdit.EndpointId is null)
+        {
+            var candidates = _endpoints.Where(e => e.Type == needed).ToList();
+            if (candidates.Count == 1)
+            {
+                _sourceEdit.EndpointId = candidates[0].Id;
+            }
+        }
+    }
+
     private sealed class SourceEdit
     {
         public int Id { get; set; }