Bad battery or alternator?

[jmig]

Tested battery and it needed to be replaced, hooked everything back up and used a voltmeter to check the alternator to make sure it was charging the battery and it read 14.65v so that is good as well. Since chasing the battery drain.

 

[kennythewelder]

There is an old trick to see if the alt is working. Start the truck. With the engine running at idle, remove the pos battery cable from the battery. (DO NOT LET IT TOUCH ANYTHING) if the truck dies, the alt is bad. If the truck keeps running, the alt is working.

 

[Eskimomann209]

Tested battery and it needed to be replaced, hooked everything back up and used a voltmeter to check the alternator to make sure it was charging the battery and it read 14.65v so that is good as well. Since chasing the battery drain.

Aye, but that doesn't tell you why your truck lit up the test light.
Disconnect the battery cable and use the leads on the multimeter to close the circuit
Set the multi to A with a line
Indicating amp D.C. Reading
Get the amp draw and TS from there