What is going on with my 98 ford expedition (eddie)?

[houstonchick7]

OK...when I try to start my truck up it just won't turn over. It will play the radio and all the lights will be on and then as soon as I continue to twist the key to start it the whole truck goes dead and it will start to click, click, click. That is the sound coming from under the steering wheel and ALL power except the clicking is gone. I found out that if I click the head lights on and off the power will return to the truck and it will re start BUT this method is no longer working. Please help!!! I have some friends saying that it is the wiring since I did buy the truck used and others are saying it might be the theft system but I am so unsure.

[spike]

It sounds like you have a bad connection at the battery cables. Check them and clean and tighten them. If that doesn't take care of it, you probably need a battery. The clicking is caused by low voltage.