Charging issues

Weird noise coming from engine a couple of days ago, I replaced all of the idler pulleys and started the truck,same thing, then it shuts down suddenly. I checked the battery voltage and it was only 6.75 volts,disconnected and clean the terminals and tested without the leads on and voltage was 12.24volts. When i connected the terminals the voltage dropped. Jumped start it with my power pack and it started but stopped once power pack was disconnected. I realize that the alternator wasn’t charging.
My question is, why does the battery voltage drop when connected.
I already ordered an alternator.

 

Could it be a bad ground?

 

Battery may be internally shorted. It’s not a good idea to run with the battery disconnected. You could hurt the alternator. 6.75v was with it not running I’m guessing. You may need both alternator and battery. Alternator stopped working, killed the battery. If you have a good battery charger, hook it up, the battery might come back. But if it’s close to 5 years old you may want to replace it.

 

Thanks, wasn’t running with battery disconnected.
Why is it that when the battery is disconnected the voltage is ok but drops when connected.

 

You might have a bad connection somewhere or really bad connection at the battery. Terminals and posts should be clean. If not clean them with a battery brush and some baking soda to clean up the acid build up.

If you have a multimeter, check ground connection. With battery disconnected, check from the ground terminal to all over the place. The bolt where the short ground cable connects to the side, block, frame, alternator case, the passenger side bare metal pieces. All readings should be .7 or lower. If the readings are higher, you’re not getting good ground.

Check the wires to the alternator. Make sure the big wire is tight, connectors snapped in good, no broken wires. It’s rare, I’ve only seen it once, the alternator could be internally shorted.

You could also check for cooling system electrolysis.

All stuff you could do before you put the new alternator in so you don’t fry it.

 

Thanks for your input

 

Disconnected there is no load at all on the battery. When connected there is a load on the battery ( it may be small, but none the less a load ). When your battery can't maintain this small load it tells me that the battery is most likely toast and ready for a replacement.

 

Thanks, tested all battery connections this morning and they are ok. Going to get a new battery this morning.
I think that i also have a bad alternator, was getting whining noise.