... I have been informed that to prove it's my glow plugs i need to put an clamp meter around the cable to check that I am drawing about 80amps that s about 20amps per plug.
No, forget all that rubbish! :-) All you need to do to check glow plugs, is measure their resistance. Remove the connection to the glow plug, and connect an ohm meter between the plug terminal and earth. If it is good, it will read between 0.7 and 1.0 ohms. Usually those that have failed will either read a very high resistance (like mega ohms) or be open circuit. i.e. you will get no reading.
If only one has failed, then you could simply replace that, but if you have more than one gone, and none have been changed in years, then it is probably time to replace the set. Get a good fitting socket and take it nice and slow, and lubricate the thread, as you wind them out. Don't over-tighten the new ones going in - they don't need much to seal and almost better loose than too tight. If they are loose and you can hear gas leaking then you can nip them up a bit more, but if you over tighten them, you will probably never get them out again!
Roy