Alternator and battery problems

KYMI ABERO

MEMBER
1997 FORD EXPEDITION
5.4L
4WD
AUTOMATIC
145,778 MILES

I was driving on the freeway one night and all of a sudden all gauges were red on my dash, the oil, water, and battery lights so I pull over and a friend helped me and we put water in the truck and then all the gauges were normal except for my battery light. The next day I notice it was still on and later that day the battery gauge went all the way down and my truck shut off. After that I took out the battery and put in a new one but my light was still on. The next day I replaced the alternator but the light was still on and I noticed that the gauge kept going down until my truck shut off again. So I went ahead and bought a brand new battery and put it in but the light was still on! Then today while driving I noticed that the gauge started going down again til finally my truck shut off again! My uncle told me I need to replace alternator elec cn, I do not know what it is but it looks like a plug with three wires coming out of it white green and yellow wires. Is that what I need to fix? I have no idea about cars.

Images (Click to make bigger)

1 Reply

CARADIODOC

MECHANIC
33,871 POSTS

The problem needs to be diagnosed rather than throwing a bunch of random parts at it. The warning light means the battery is not being recharged while driving, not that the battery is bad.

We can skip the first few tests as we already know the generator is not working. The first test is to see if the "Battery" light turns on, and that we know already. That's the turn-on circuit for the charging system. We also know the system isn't working. Now we get to figure out why. If there's a reason to suspect the three-wire electrical connector, tell me what was found with that, otherwise we'll just approach this with normal diagnostic steps.

You're going to need a test light for these tests. A digital voltmeter will work too, but for this type of problem, a test light is cheaper, faster, and can be more accurate. Here's a link to a guide that explains how to use one, if you need it:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

I posted the wiring diagram for this circuit. Don't panic if you don't know how to read it. The second photo shows the back of your generator and where to take the voltage readings. The first one is up at the top on the large output stud. You should find 12 volts there with the engine not running. It's less common to find that missing, so we'll skip the rest of that for now. The more common problem is a blown fuse. To find that, you'll need to check for 12 volts on the orange / light blue wire. That's an orange wire with a blue stripe. Many people will pull out the three-wire plug, then check on the terminal, but it's faster and more accurate to just poke the test light's probe through the rubber seal right next to that wire while the plug is still plugged in. This one should also have 12 volts all the time. If that is missing, we'll need to find the 20-amp fuse and check that. Ford put that in the under-hood fuse box on other models. Yours is listed differently, so I'll have to find a drawing showing where it is. It looks like it is attached to the fuse box, but outside it.

Let me know what you find at those two points.

Images (Click to make bigger)