Check all the connections between battery and alternator, chances are there is a loose connection some where.

 

we couldnt find anything but after gentle tap with hammer no charging light went of immediately...and battery was fully charged until we got home...

 

Sounds like you need a good alternator and then you can put the hammer away.lol

 

If thats the case, likely the alternator brushes are shot.

 

Sounds like the brushes on your slip rings are worn down to the point where they brush springs don't have enough tension to give you good electrical contact. Those brushes are replaceable if you can find a place that knows how to tear down and alternator.

 

well...while waiting for new alternator...taping doesnt work anymore...i have lost all electrics today again within 10minutes...and this time after abs light come one laud grinding noise started...only when moving.
got home as i was only 1mile away but not pleased with situation...

 

and strangly...after 1hr truck started with no problem...baterry shows 11.5V....2nd restart and even baterry gauge showing almost 12V...truck does not have enough power to start...
what im missing here?

 

Recharge the battery it's weak.
.

 

This is not rocket science.
When you are measuring the battery voltage with a real voltmeter (not the dash meter) is the engine running?
Where exactly are you measuring the battery voltage?
Try measuring the battery voltage with engine off, headlights on and heater blower motor on high. Leave all on for a couple minutes.
If the voltage dips well below 12 volts DC the battery is shot, not charged properly or there's a high impedance electrical connection somewhere..

1. Important! Have you taken the battery to a shop to have it tested under a load tester preferably after recharging it with a stand alone battery charger?
If the battery checks out ok then:
2.Have you checked the battery terminals to make sure they're not loose, corroded or worn out enough not to make a good high amp electrical connection even when firmly tightened?
3.Have you checked the battery's (-) ground terminals to the chassis/engine making sure they're not corroded or loose?
4.Have you checked the electrical connections to the starter motor for corrosion, looseness, etc.?
5. Measure the alternator output voltage with engine running across the battery clamps not the posts. If well under 13 or so volts then the alternator, its connectors or the battery clamps are at fault.

What do you mean by:

 

He was tapping the alternator with a hammer to get it to charge.