glow plugs
 

what the easyest way to test your glow plugs and also what are some common things to look for when u suspect bad ones

i would test the glow plug relay first. these are a common problem

Read through this thread. It's long, but will probably answer all of your questions. That's why it's a sticky at the top of the page. Long, but great info. Here's the link:
https://www.ford-trucks.com/forums/s...d.php?t=421710