Save yourself lots of time and money and get your local garage to test the pressure with a mechanical test gauge before doing anything else. As a garage owner I have seen people often forget to check the basics first.
Once you know whether your engine has pressure it will determine whether its a simple thing like a faulty gauge or sender or more serious engine problems. Often the electrical parts will develop faults and on e types it is a known issue.
Hope you find our engine is good
Tony