I have a 2006 F-150 5.4L 2WD that I recently purchased and I have an intermittent problem in starting the truck. 3 times in the past two months I tried to start the truck but all I get is a buzzing sound out of the front passenger floor area. I let go of the key and I hear a clicking sound from the passenger area fuse and relay panel which may last anywhere from just a few seconds to a couple minutes and then it stops. Sometimes after the clicking stops I can then start the truck. Sometimes I have to wait as long as 15 minutes but the truck starts up. The battery seems strong as it never struggles to turn over the motor. I've tried pinpointing the relay that is clicking and it sounds close to the starter solenoid relay but it's hard to isolate. I've tried swapping the relays and the problem persist. The only solution seems to be just wait a few minutes and try again.

Any thoughts you may have are appreciated.

 

Have you had the battery load tested?