87 300TD cranks wont start glow plug

[gatess]

Our beautiful 1987 300TD will not turn over. Our 15 year old son, soon to be 16 and driving went to start the car(Titan) we name all of our cars. He forgot to let the glow plug warm up, now Titan who has been starting and running great, will not start? The glow plug light is not coming on now but its 70+ degrees outside. I tried cranking for 30 seconds, no start, let starter rests 15 minutes, cranked again for 60 seconds and still no start. I feel like this is an easy problem to fix, I just don't know what it could be?, with the hood up, you can hear the relay(I am assuming its the relay) Click when trying to start Titan. Any and all help from the community would be greatly appreciated! Thank you, Sincerely, Jerry and Dana Gates