Alternater Question

juke joint johnny

juke joint johnny

Well-known member
My pickup has a 12 volt negative ground alternater on it.Think it's a 3 wire one out of a ford van Put on by a previous owner .

I always close the tap and run the gas out of the fuel line before I switch it off

Last nite I forgot to turn the ignition switch off ,and closed up the garage for the nite .

So in the morning I can't find my key's because there still in the switch . by this time the battery is dead .
So I charge up the battery and the coil was not burnt out it started OK

But the alternater does not seem to be charging . So my question is,
Could the switch being on all nite have burnt out something in the alternater??? might be time to go back to the original generater!!!
thanks in advance for any help

John Cochran
 
possible try charging the battery and then see if the alt will charge, it takes a small amout of juice to activate , if yours is bad go to a chevy 3 wire, plentiful, cheap and easy to hook up
 
It may have an external regulator. Check that. Replacement Ford alternators are as cheap and plentiful as the Chevy. If it needs replacing, take the old one off and match it with a new one. Then it's just lug and play. Switching brands may mean fabbing new brackets.
 
you can ground out the alternator and make it charge. Sometimes if the battery goes dead or if there's a disconnect switch that's been left in the off position, the alternator will forget it's polarity. I bet this is what's happened in your case.
 
:"the alternater does not seem to be charging"

If the battery is at full charge your ammeter will read zero. Put a voltmeter on the output stud, other lead to ground. Not running, you should see about 12.6V with a full charge battery. Running at moderate engine speed (~1200 rpm) you should see 13.8 -14.8 depending on the internal regulator setting.

If it is a 10/12 SI 12V neg alternator there should be a test tab visible through the back. Shorting the tab to the frame by inserting a small screwdriver should drive it to max output. Warning: make sure you have no lights on when doing this- they may pop from the voltage spike. If this sends the voltage up but when released it drops back to 12.6 battery voltage you have a bad internal regulator or diode(s), likely the trio.
test-GM-10si.png
 
juke joint johnny said:
My pickup has a 12 volt negative ground alternater on it.Think it's a 3 wire one out of a ford van Put on by a previous owner .

I always close the tap and run the gas out of the fuel line before I switch it off

Last nite I forgot to turn the ignition switch off ,and closed up the garage for the nite .

So in the morning I can't find my key's because there still in the switch . by this time the battery is dead .
So I charge up the battery and the coil was not burnt out it started OK

But the alternater does not seem to be charging . So my question is,
Could the switch being on all nite have burnt out something in the alternater??? might be time to go back to the original generater!!!
thanks in advance for any help

John Cochran
Click to expand...

What makes you say that?
 
Well it has an idiot light on it instead of an ammeter, it used to go out when it idled fast but not now . It's something else put on by previous owner . it always worked so I never changed it .
 
If it is the alternator MikeK pictured do not insert the screw driver too far.

If it has an idiot light it should be tied to the diode trio output at the VR plug position 1 or R. If the light goes off (did) under fast idle it suggest a small bulb.

if there is a wire hooked to 1 or R, with the engine running jump between the battery post on the alt to that position, just touch it quickly. The engine should idle down if the alt comes on line.
It should not have hurt the alt. Remember only 1-R is tied to the key.
 
Thanks everyone who replied to my post .
We moved house last week so I have a big "Honey Do List"

BUt I hope to soon get out in the garage again to try out some of the ideas you came up with.
John Cochran
 
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