I couldn't start my truck last night(08 f150 xl) and thought it was due to a weak battery but when i tried to jump it it still would not start i had juice to all my lights radio but when i went to start it i lose all juice Im thinking its the alternator but wouldn't it at least start when jumping it. Thanks for any comments left

 

I'm not an expert and could be wrong, but if the alternator isn't working then it won't start because the battery is just to get it started then the alternator kicks in and keeps your truck running while it keeps the battery charged. what type of sound is the truck making when you try to start it? Is it trying to start? Or is it making no noise at all?

 

The Alternator's job is to charge your battery and run all the Accessories while your truck is running...the battery strats your truck...get a new battery.

 

If the battery is completely dead, you may want to put a charger on it, or let the donor battery/vehicle's alternator your attempting to jump off of charge up your battery. A completely dead battery will not start your truck immediately from a jump.

It's that or your starter is sucking a high amount of current to start. I think it's your battery though. It's so dead that a jump will not work. How old is the battery?

 

Most auto parts stores will load test and charge your battery for free. Start there

 

He stated he had a weak battery to start with...

 

Take your battery out. Get it tested.

If it was your alternator, you'd have symptoms.
My mom's ride has a bad alternator. Symptoms include: car turns at low idle under heavy load (high AC etc), battery drains itself, lights flickering inside, idle dropping when in gear, etc.

FWIW, the testers at autostores are VERY inaccurate. Said the alternator was good, I took it out, took it to a bench where it failed. Good luck

 

it ran fine when i got to my mothers house i turned it off for a minute then tried to start it it wouldn't start when i hooked jumper cables to it let it charge for like 5 minutes and still wouldn't start while jumpers were connected lights were bright seemed like it had plenty of juice until i went to start it then everything would just go out the starter was clicking and engine seemed to want to turn over but just barely the battery is about a month or so old

 

Check your cables...frame ground/starter connections....you didn't tell us the battery was only a month old the first time...you said it was weak...

 

You can spend a whole lot of money and it could be very simple like tech said. Just because the radio and a few lights come on does not mean your battery/connections aren't bad. Yes the starter requires alot of power to start your truck. Be advised, when you take your battery in to be tested at the parts store, the best test is done when the battery has a full charge. After the battery and connections it is time to go deeper. Then and only then check the alternator. Check the connections first and then have it tested by the parts house. Do not just throw money at it.