1999 f-150 v8 triton XLT 4.6L
I got a new alternator and battery and my truck still wont hold a charge? Please help with any and all pointers you can giv.
Thank you

 

Check the voltage across the battery with the engine running. It needs to be at least 13.5 volts.

 

Yes there is enough volts, is there a mega fuse or a link fuse that could have gone out? Thank you for your help

 

If you have at least 13.5 volts (14 preferred) at the battery with the engine running, you don't have a charging problem. You have a bad battery or a current drain with the engine off.

 

The Battery is new and was checked in a similar truck. tried 2 other batteries before buying the new one? What would cause the current drain? Is there an easy way to check ?

 

Yes. Follow directions, make the recommended tests, and post the results. Do not try to analyze the data yourself, leave that to someone who knows what they are doing.

 

could it possibly be the gem module?

 

BTW last month had a diagnostic test done and it said I needed a tune up and yesterday it would read at all?

 

this help is really appreciated

 

Very first thing; is the charge light on the dash?
If yes there is a charge circuit failure, If no there is a drain.
Normally with the engine running and battery up to full charge you should se very close to 14 volts, no less.
After cranking you should see close to 15 volts for a short time that falls back to 14 as the battery take its charge.
How long it takes to drain down at a point the engine cranks slow is some what of an indicator.
You have to observe these thing if your going to solve the issue.
As of the moment it all guessing that isn't worth a Hoot.
Testing and observing is the only way.
You already spent money on un needed parts by guessing.
Good luck.

 

Yes the charge light stays on battery drains really fast . would it be the fusible link or gem module?

 

If the charge light stays on I don't see how the battery would be reading proper voltage. Put a meter across the battery terminals with it running, how many DC volts?

 

We needed to define the issue first.
NO the fuse won't be open for 'drain'.
Current doesn't jump through the air.
The charge light is telling you the alternator is not outputting, fuse or no fuse open or good.
A fast drain like you indicate is coming from the Alternator through the megafuse.
It is either the diode stack or the regulator has not turned the field winding off.
How to test
On a fully charged battery, remove the heavy lead at the Alternator "in a safe manner" because it's hooked to a charged battery on the other end. And not short the end to metal around the area.
Re touch the lead connector to the Alternator terminal monumentally.
Doers it spark noticeable?
If yes the alternator is the problem drain. It has to be open circuited when not being driven by the motor.
Note: the dash charge lamp is powered through a fuse and ignition switch in the on position so we know that circuit is good.
Any other cause of a drain that 'high'[ normally would blow its much smaller fuse.
So anything is possible until you find the cause.
Also an Alternator that feels warm long after the motor has cooled is suspect for the same reason as above..
Good luck.

 

Thank you for response I am learning.
so do I check the mega fuse ? or the the fusible link to the battery.

 

You can if you want to.
Re read the second and third line of my reply above.
It has to be good to pass current! from the battery.
Good luck.