my 2008 f150 is acting as though it has a bad battery or alternator, however when I take it in to have checked out the battery and alternator come up good....what is happening is when I go to crank the engine sometimes it makes a clicking noise or is real sluggish at starting, but every time it starts...and if I turn the truck off and try to crank it right back up it starts immediatly... Was told it may be a starter solenoid or a bad cell in the battery... if its the solenoid how can i check it and where is it located?? any help would be greatly appreciated as I am getting a headache fooling with it...