90 ford f150 5.0 auto. Brand new battery, when turning the key, there is a pretty loud buzz/vib at whatever the little round thing (solenoid? relay?) on the firewall near the battery where the positive cable runs to. I have cleaned the terminals, and cleaned the connections at the round thing. Any other things to check, ran out of time or would have checked the ground connection. How do i diagnose a bad starter in the truck?

 

Disconnect the battery. Remove the starter and take it to your local auto parts outlet. Have them bench test it on thier machine, for free. Let them know how it behaves, and they will test it for you.
Hope this helps.

 

Internet search suggests it could be a bad cable or ground connection - will check all of those this evening if weather holds before pulling the starter

 

Wiggled ground connection to battery - turns out cable was loose in the terminal. Truck started right up, hope to clean it and reclamp it if possible, if not get a new ground cable and install it this weekend