ok so after that "hurricain" we had i started up my truck n my battery light was on so i turned my steering wheel to make sure i had power steering so i poped the hood serp was good so i drove it home volt gauge was reading normal ecept i turned on my defroster n the gauge droped alot but not into the red. so i drove 2 hours back to my house no probs so i had a spare altinator that i knew was good slapped it on went out for a wile then came back on. so i cleaned up the cables and i started the truck and pulled the positive off the battery n it stayed runnin n i took a test light from the ground to the positive battery cable "still off the battery" and its chargin
im stumped

if you didnt know i have 90 f150 4.9 t18 3.55 4x2

 

I know this may be dumb of me...but is their liquid in the battery?
I ask cause I have heard of some people having the light come on and they were low on fluid...just a thought but I can be wrong

 

yeah it does it less then a year old and i always check to be sure they are full its part of my monthly inspection

 

Go over to Autozone and get the battery and alternator tested. They can do it free in the parking lot.

 

hahaha i dont know about ware u live but ware i am my 1 year old knows more about cars then they do but my batterys less then a year old " ive never had them go that quick" and the altinator was off of a working truck that had no problems

 

Maybe so, but they DO provide that service. It doesn't take a rocket scientist to use a handheld battery/alternator load tester.

 

If you checked the pos cable with it disconnected, it's still going to show the output voltage of the alt because you still have to put the neg side of the meter to grd. Sounds to me like the batt is on its way out as the light comes on when under a load and you already eliminated the alt.

 

Do you have a voltmeter?

Adrianspeeder

 

yeah i got a volt meter and my uncle has a shop about 2 miles away he has all the stuff i dont

i agree its simple handheld device but i mean these guys cant tie there shoes i refuse to get anything from the store