You can easily test code using Debug.print. It puts a run's result into Immediate Window. IF not shown, set it in View menu.
I did not see that you had removed the Case Else condition when I posted the revised code in #19. I also modified that case check since 1 to 7 would allow 1.1, 1.56 and such. I rename the file to Ken.xlsm to make this more clear. Here it is:
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1 '[ken.xlsm]H-erne'!$D$3 '[ken.xlsm]H-erne'!$E$3 '[ken.xlsm]H-erne'!$F$3
2 '[ken.xlsm]H-erne'!$G$3 '[ken.xlsm]H-erne'!$H$3 '[ken.xlsm]H-erne'!$I$3
3 '[ken.xlsm]H-erne'!$J$3 '[ken.xlsm]H-erne'!$K$3 '[ken.xlsm]H-erne'!$L$3
4 '[ken.xlsm]H-erne'!$M$3 '[ken.xlsm]H-erne'!$N$3 '[ken.xlsm]H-erne'!$O$3
5 '[ken.xlsm]H-erne'!$P$3 '[ken.xlsm]H-erne'!$Q$3 '[ken.xlsm]H-erne'!$R$3
6 '[ken.xlsm]H-erne'!$S$3 '[ken.xlsm]H-erne'!$T$3 '[ken.xlsm]H-erne'!$U$3
7 '[ken.xlsm]H-erne'!$V$3 '[ken.xlsm]H-erne'!$W$3 '[ken.xlsm]H-erne'!$X$3
That looks like what you wanted in #1 except for X3. I fixed that too in the code below. Why was it "wrong", it wasn't. See your code:
Private Sub TextBox1_Change()
Sheets("H-erne").Range("D3") = TextBox1.Value
End Sub
Private Sub TextBox2_Change()
Sheets("H-erne").Range("E3") = TextBox2.Value
End Sub
Private Sub TextBox3_Change()
Sheets("H-erne").Range("F3") = TextBox3.Value
End Sub
Private Sub ComboBox1_Change()
Dim r As Range, i As Integer
Set r = Worksheets("H-erne").Range("D3")
Select Case ComboBox1
Case 1, 2, 3, 4, 5, 6, 7
Set r = r.Offset(, ComboBox1 * 3 - 3)
For i = 1 To 3
Controls("TextBox" & i).Visible = True
Controls("TextBox" & i).ControlSource = r.Offset(, i - 1).Address(external:=True)
'Controls("Label" & i).Caption = r.Offset(, i - 1).Address(False, False)
Next i
If ComboBox1 = 7 Then
TextBox3.ControlSource = Range("Z3").Address(external:=True)
'Label3.ControlSource = Range("Z3").Address(False, False)
End If
Case Else
For i = 1 To 3
Controls("TextBox" & i).ControlSource = ""
'Controls("Label" & i).Caption = "No Link"
Next i
End Select
'Debug.Print ComboBox1, TextBox1.ControlSource, TextBox2.ControlSource, TextBox3.ControlSource
End Sub