Strunt i, jag fick det :
Create trigger [dbo].[TR_AUDIT_TESTAUDIT]
ON [dbo].[testaudit]
AFTER INSERT, UPDATE, DELETE
AS
BEGIN
SET NOCOUNT ON;
declare @action nvarchar(1)
set @action = 'I' -- always I
if exists(select top 1 1 from deleted) and not exists(select top 1 1 from inserted)
set @action = 'D'
if exists(select top 1 1 from deleted) and exists(select top 1 1 from inserted)
set @action = 'U'
END