1998 Ranger with a charging issue

[01rangerxl]

I don't have solid details on this or what the initial problem was...trying to help my cousin out over the phone.

The vehicle is a 1998 Ford Ranger 4.0, somewhere around 200K miles on it. No rust, AL truck all its life.

Apparently it was having charging issues and the battery light was coming on. My cousin started by replacing the battery, then the alternator. The battery light remained on after replacing both of those. If the wiring harness (not the main wire) is unplugged, the battery light goes off. The new alt does test good when bench tested at the parts store. He said the main wire is showing half a volt with the truck running when tested with a multimeter.

I'm guessing a fusible link or bad ground, but I don't know. Electrical stuff is not my area of expertise, and of the Rangers and Explorer I've owned, none ever had charging problems. Any ideas on what might be the issue are appreciated.

Cliff notes: new alt, new batt, batt light still on, but goes off when the harness is unplugged (not the main wire). New alt bench tested good at the parts store.

 

[JHZR2]

Which wire? The exciter wire that uses the battery bulb to get the alternator going?

Bad ground or bad short seems sensible, but need to understand the wire. 0v wouldn't let the truck crank or the ecu boot up.

 

[01rangerxl]

By "main wire" I mean the heavy gauge one that bolts to the post/stud on the alt. Not one of the ones in the little plug in harness.

From what I can gather, he's getting the voltage reading from that big output wire, not one of the ones in the little plug in harness.

Not sure if the truck has been cranking on its own...from what I have been told so far, it did start up and run on its own, the battery light just stayed on.

 

[yonyon]

Do you actually have low charging voltage or just a battery light on? A battery light on with good charging voltage can be caused by a a problem with the PCB in the cluster.

Assuming low charging voltage: unplugging the alternator turns the light off because the green w/ red wire is what turns the light on. No connection on that wire -> no light. With your new alternator that bench tests good you need three things: You need a good connection from the B terminal (big wire) to real battery B+. You need B+ on the A terminal (yellow with white tracer wire) because you don't have a blown fuse. You need the new alternator to not be improperly assembled with the wrong voltage regulator (wants GND instead of B+ to turn on) on it.

...maybe...I think.

 

[The_Eric]

If the large gauge wire on the back of the alter isn't reading at least battery voltage, there's where you need to start looking. There should be a 100 amp fuse in that circuit. Also check all connections along that wire.

 

[punisher]

Check the charge fuse in the underhood fuse block. If it looks OK, wiggle it while keeping an eye on a voltmeter on the battery.

 

[JHZR2]

Originally Posted By: The_Eric
If the large gauge wire on the back of the alter isn't reading at least battery voltage, there's where you need to start looking. There should be a 100 amp fuse in that circuit. Also check all connections along that wire.


+1 big wire as defined sounds like the culprit.

For a fuse to go, it would need to be a big deal. My guess is corrosion destroyed the wire from inside out.

There is probably some other 12v source connected that excites the alt, but it's not correctly connected, soonly some small delta-voltage is observed.

Notionally the battery voltage should be dropping quick when running.

 

[yonyon]

The_Eric is right. The big wire must have battery positive at all times or something nice and big is not connected.

 

[01rangerxl]

Originally Posted By: The_Eric
If the large gauge wire on the back of the alter isn't reading at least battery voltage, there's where you need to start looking. There should be a 100 amp fuse in that circuit. Also check all connections along that wire.


Never did look at the truck myself, but apparently this fuse was blown along with some others. Apparently after replacing the fuses, everything is working normally.

Thanks for the responses guys.

 

[JHZR2]

Big issue there. Why is a 100A fuse opening???

 

[01rangerxl]

That I don't know (haven't looked at the truck). My cousin is hoping the fuse blowing was some result of the original alt going bad. We'll see what happens.