truck wont start, stranded...

[91explorer1009]

(1991 explorer sport)-I went to start my truck after work tonight, and it was just clicking. I have lights when I turn the key and power windows and such, so I dont think its the batt, it is fairly new. When I go to start it I get a loud fast clicking and it doesnt turn over. Just continuous clicking almost like a machine gun. I had the starter replaced about 2 yrs ago so I dont think it would be that, but I don't know for sure. I also was with a friend and he went under as I tried to start it and the clicking sounded like it was coming from this little black round cylinder next to my oil pan. He tried tapping it ligthly with a hammer and sometimes it would sound like it was trying to turn over for a second, but continued clicking rapidly with no success. I am trying to look stuff up in ,my haynes, but I don't know what to do. I am now without a truck for the moment. Please help.....

 

[Papa]

Check the battery terminal voltage under load; it should not drop below 9.5 VDC after cranking the engine over for 15 seconds if you get that far. You may need a jump-start.
Poor electrical connections will cause the solenoid to chatter as if you have a dead battery. Bad cables will also cause similar problems.