I have a 2002 F-150 that will not start. I jumped my riding lawn lower with my truck in October (truck started fine) and left my keys in it in the on position. I tried to start it 3 days ago and no juice from the battery. I replaced the battery today, but it will not start. The instruments in the dash lit up when I tried to start it with the new battery but it would not turn over. Then nothing, no lights. Any time a door is open, hood is open, or when I turn on a dome light (even though I have no power) a relay clicks. If I close the door/hood or turn the light back off there is not a click. I open the fuse panel and all the fuses are good. I have 2 smaller yellow relays in the top 2 left slots, the bottom relay is the one clicking. I swapped the relays and the bottom relay still clicks when the door is open. I think I have a open circuit when the door/hood is open but I looked at the cabling and I don't see anything out of the ordinary. Starter cabling looks good. Any ideas to fin the problem, I need to start driving my truck during the winter months. Thanks for your help.

 

when you say it wont start, you mean it wont crank over?? I question the battery. Is it charged up good? Will the head lights turn on bright? With key on, step on brakes, you go brake lights? I would take a volt meter and check the battery voltage. Sounds like you let the truck set quite some time... any corrosion on the battery terminals? Are the wires good? Good ground strap?

 

If all is well with the wires and the grounds and the battery voltage checks out may also have to check the solenoids, may have one on starter and one on the firewall I have had both go out after low battery in the past with my 99 5.4l. Quick check with jumper between the two terminals. But my bet is on the voltage of the battery.