I would highly recommend haveing a qualified tech look at it. You should be changing you oil every year at the least. Babying a diesel is the worst thing you could possibly do to it.
Which alarm actually went off? If it's going off constantly it may be the
harness connection or not. If you have a problem somewhere else and asume it electrical your could be in for a rude awakening.
Do yourself a favor ticker around if your handy, if not have somebody reputatable look at it and get a good Diesel book. Peace of mind. Run that engine hard for an hour a month at the least if you don't use it much under load. Once the problem is found. Good Luck PEACE