jw lee

Got a 94 f150 4x4 alternator was tested at advance and is charging at 15.7 volts when you disconnect the negative battery cable it chokes down and catches back up but is still charging at about the o on normal if you turn the lights on and back off it chokes for a second then catches up and starts charging about 15 volts but if you put the cable back on it goes back down please help

Chris_1

iTrader: (1)

Huh ? your post is a little confusing, but at a guess I'd say at least check all your connections (especially the grounds) and I believe there may be a fusible link in that circuit that would be worth checking.
That's just guessing, but it's somewhere to start

jw lee

Well when I say chokes down I mean the motor basically it'll charge like it should for about 5 minutes With the negative battery cable off but as soon as you reconnect the negative battery cable it stops charging

Stu Cazzo

Dead cell or cell shorting out in battery. Of the past 30 years of my driving vehicle owning life...I'd say 95% of my starting / charging / it needs a boost problems were always battery related.

Swap out the battery and problem probably goes away.

Just call me Sean

iTrader: (1)

Stop disconnecting the battery when it's running, you're going to fry something. You don't test alternators that way anymore.