why won't my truck crank over what can it be help please on 2002 Ford Expedition

I changed the starter n the alternator they were bad when I tested them I also change the solenoid on the firewall n I got a new battery that also went bad but it wont start it just clicks at the solenoid. was running fine it just shut down while driving. also i hooked up the scanner n it won't link to it. please help

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1 answer 2 comments
double ck all your battery and cable connections, sounds like you have a bad one. also ck grds
done checked all connections n no luck does any one know what sound does it make when the its not reading the chip on the key ? my just just clicks at the solenoid on the firewall a loud tack tack tackbut it wont crank or anything else well lights and radio work fine please help thanks
its not you key if your solenoid is clicking. you have a BAD connection,12v is not getting thru