I've had my battery light come on three times in my 1999 Ford Ranger 4x4 with the 3.0 and 4R44E transmission. I assumed the alternator was bad again, so I took it off and went to AutoZone to replace it. It's done it two more times, with the truck running. The battery seems to check out, I just replaced it 6 months ago. What else could be the problem? AutoZone says the alternator is fine, there's is no corrosion on the terminals, and both connections are solid.
I fixed it. The mega fuse was bad. I've never heard of a 175 Amp fuse. I had no clue where that would be. My friend helped me, and we were both scatching our heads. Then, after we suspected the mega fuse might be bad, after viewing a YouTube video on where it is, that was the problem.
What do you know. I punched "ford ranger 1999 charging system schematic" into a web search and this was the first result.
Not the first time this 'easyautodiagnostics' website has come to the rescue. Excellent site. Jack recommends it all the time.
https://easyautodiagnostics.com/ford/3.0L/alternator-wiring-diagram-1
'I' is the indicator circuit. There's some wiring and a fuse to check there.
'B+' is the high current terminal that actually charges your battery
'A' is feedback for the voltage regulator. It is sensing voltage on the high side of the mega fuse to set the correct voltage.
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All 3 should be at around 14V when running, at every point in the circuit, except the grounded side of the indicator light.
What's the actual voltage when the light turns on? Is the voltage regulator built into the alternator or does your PCM control it?
I used a multimeter and it shows around 12.15 v with the engine running.
Obviously not good. Do you have a good ground between the engine and chassis?
Before I took anything apart, I found certain sweet spots where the RPMs would keep the battery light off, which zeroed in that it's a faulty alternator, at least I thought it would be.
Might be a voltage regulator problem as well. I don't know if that model has the regulator built into the alternator or if output is externally controlled. (I've seen it done either way on vehicles of that vintage.)
Also check wiring carefully. I once had a problem similar to that and it turned out that a thin wire connected to the alternator was internally corroded at the connector even though it looked OK on the outside.
My fiancée found a fuse for the voltage regulator, I'll check that.
We replaced the fuse, it still does it. The only thing I can think of at this point is it's not properly grounded anymore due to corrosion somewhere. When I originally replaced it a year ago, the battery light would come on intermittently, then it stopped after a week or so.
If you have access to a factory shop manual you might want to see what the factory procedure is for testing the charging system. It's probably more complete than whatever method AutoZone uses to test alternators.
they just hooked it up to some kind of machine and tested it. Lol. I couldn't observe anything because it was hidden from view. I still only have one useable hand, or else I'd do some more troubleshooting.
The only thing I can think of at this point is it's not properly grounded anymore
alternators are usually grounded through a strap that connects the engine block to the frame or body. Same with the battery.
You can test both connections at the same time, by measuring resistance between the alternator case and your batt neg post, or voltage drop while it's charging.
I used a multimeter and it shows around 12.15 v with the engine running.
I assume that was on the battery. I wonder what the voltage was on the alternator itself.
I can't understand how it tested fine when it clearly doesn't charge.
I couldn't find any data about your charging system, other than it came with a Motorcraft GL8706RM generator
My battery was made by Rural King and is slightly larger than the battery pan. My father-in-law put in the piece of wood just now. It did the same thing before, though. The clamps aren't there anymore. They both rusted off. Lol. He did the work, and he accidentally took off the positive cable, not the negative. I was supervising and I told him to remove the negative. I may have fried something. The voltage regulator wasn't just a fuse, it was more of a relay type thing, as opposed to a straight fuse.
By the late 1990s some vehicles were regulating alternator output with the PCM. My 1999 Cherokee is like that. (For those old Jeeps there is a way to rig an external voltage regulator from earlier models if the PCM circuit fails.)
removing the positive cable won't hurt anything as long as you don't wave it around and touch parts with it.
Regulators aren't fuses or relays. They are an array of diodes to rectify the current plus a solid state silicon voltage regulator. It basically shunts current that exceeds a pre-set voltage. (this was the old style before computer regulation)
Sparks flew everywhere when he attempted to hook the battery terminal back up, lol.
that's normal
I'll explore some more when it stops raining in the next couple days. It's supposed to get below freezing for the first time this season, tonight.
I know. It got really cold.
I have 3 garages, but they're all full of stuff right now from the previous owners, unfortunately.
sell the stuff. Then put a heater in there.
I did some poking around. Only the black/orange cable emerges from the alternator itself. The fuse box itself is in between the orange/black cable and the red cable. There's a mega fuse between it and the alternator (175 amps), as well as a 30-amp fuse. I know the fuse is good. I swapped it with a known good fuse at 30 amps and started it. Same thing. I'll charge the battery with a battery charger and go to AutoZone with a fully charged battery and have them test it on the vehicle. I highly doubt I blew a mega fuse by touching the positive with the negative already on the battery.
You can't hook up a multimeter without unhooking the alternator.
you can with the right tools
Interesting, learn something new everyday. I still hate electronics, structural engineering is my forte, because I can see things with my eyes, electrical engineering is another story. I married an electrical engineer, lol, so I married to my and her advantage she doesn't work on cars, though. She just puts gas in the car, it's up to me to do maintenance.
well this IS an electrical engineering problem. You married just the right person for the job!
Tell her the alternator is just a rectified and smoothed AC power source. She should be able to figure the rest out if you just show her the diagram, and where everything is on the car.
The battery light is still on.
it's not like it's operated by computer. it can't be a bad indicator. According to the schematic, the only possible way for the lamp to turn on, is if there's a difference in voltage between the alternator 'I' terminal, and fuse 15 (have you checked it?), which is the key-on hot circuit. So I would measure those.
Like I said before ....
I wonder what the voltage was on the alternator itself.
I checked fuse 15, it's fine. The alternator charge level reads just fine before I start the truck. I'm gonna go to AutoZone tomorrow to check out the alternator on the truck with a tool. I'm still semi-restricted on driving, even though I passed my test.
what I meant was, did you measure a voltage on fuse 15 when the key is on.
> "The alternator charge level reads just fine"
but did you measure it RIGHT at the alternator terminals? (A, B, & I)
No, there's only one cable, the orange/black cable. The rest are internal to the alternator itself. I was also never into electronics, lol.
I think I know what you mean. If I'm interpreting this diagram correctly, one lead should be on the bracket that holds the cable in place. The other needs to be grounded, so anywhere else on the truck. Then compare the two at the fuse.
oh you have a "one wire" alternator. The diagram isn't valid then.
It would still be useful to see the voltage at the alternator stud.
I'll try that tomorrow.
There's only one connector. I know, because I've taken it out at least 5 times at this point, lol.
So it has a 1-wire alternator from the factory? Or was it replaced at some point with an aftermarket alternator? Looking up photos of the stock alternator for your vehicle it looks like it has a multi-wire connector plus a terminal stud on the back.
Justin, I got lost trying to keep up here. Have you determined that there is BOTH a BLK/ORG wire bolted to the alternator B+ stud AND also a separate wiring connector plugged into the alternator?
Yep, there are both a wire and connector.
So leave the BLK/ORG wire bolted to the alternator B+ stud and just disconnect the wiring connector
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Turn the key to ON and make sure the BATT light on the dash doesn't come on
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Then, while you have that connector unplugged, check for power on the connector terminals that have the YLW/WHT wire going to it (should have power always)AND the LT GRN/RED wire (should have power in Run and Start).
I may try that tomorrow; it gets dark early this time of year. The AutoZone guy says it's either a faulty alternator or there's a short to ground somewhere. Most probably it's in the actual connector. That connector seemed pretty worn when I was assisting with the replacement. I only have one hand right now which is driving me up the wall. I got a replacement alternator, and I might order a new OEM Motorcraft connector and wiring as well. I'll see which side of the alternator it's on.
Just make sure the problem isn't voltage drop on that YLW/WHT wire. So even if there's Power there, run a jumper wire from the battery positive post to a backspin on that YLW/WT wire on the alternator connection and then check the charging rate
I made sure both the terminals were secured, and the cables themselves, I have aftermarket battery cables, and the positive terminal cable itself was loose. That's fixed. The battery light is still on. I'm about at my whit's end, lol.
The alternator's BLK/ORG cable goes to the underhood fuse box, and then through the 175 amp "mega fuse" to the battery.
There's a connector, on the alternator, to the alternator's internal voltage regulator (fuse 15 goes to one of the wires. The 30 amp ALT Fuse goes to the other wire).
Find that connector and disconnect it.
Turn the key to ON and make sure the Battery Light doesn't come on.
If it does then there's a short to Ground on the LT GRN/RED wire between the dashboard and the alternator connector (I) ((refer to the diagram above that @imperator posted. It's either accurate or close enough. They stuck some fusible links in the circuit in some model years but that doesn't matter)).
While you have the connector unplugged check the voltage at the YLW/WHT wire (alternator A terminal in above wiring diagram). Should be battery voltage (always).
Reconnect the connector to the alternator.
Then, assuming that you checked for voltage drop between the battery Positive post and Alternator B+ terminal (engine running) AND you checked for voltage drop between the alternator case and the battery Negative post, why not see what happens to the charging voltage at the battery if you use a jumper wire and jump from the battery positive post and a backpin at the YLW/WHT wire ("A" connector terminal) at the alternator just to rule out corrosion/resistance "voltage drop" in that part of the wiring
Justin said above that there's only one conductor coming from his alternator.
I maintain that there's another wiring connector on the alternator (on its internal regulator) besides the B+ connector from the alternator B+ terminal to the fuse box's mega fuse.
If not, where does fuse 15 and that 30 amp ALT fuse he found go to?
There's only one connector. I know, because I've taken it out at least 5 times at this point, lol.
I'm thinking the same thing, I may just take it into Blair's if I can't figure it out.
There's only one connector. I know, because I've taken it out at least 5 times at this point, lol.
Right, but one connector is not the same thing as one wire. A connector can have multiple terminals.
There's a mega fuse between it and the alternator (175 amps), as well as a 30-amp fuse.
for example, what is connected to this 30 amp fuse?
My fiancée found a fuse for the voltage regulator,
is the regulator not part the alternator?
Apparently not. I misspoke. There is a connector and a stud that both hook up to the alternator. One is a stud that hooks up to the orange/black cable, there's a physical connection that occupies the other three cables. Sorry about that
You can't hook up a multimeter without unhooking the alternator.
The alternator and the regulator are separate from each other.
I don't know if this will help, but here's a pretty detailed explanation of how the charge light works and its role in excitation of the alternator field coil, along with some troubleshooting information:
https://www.practicalmachinist.com/forum/threads/alternator-idiot-light.78415/
If you look at the wiring diagram provided by @jack62 notice there is a resistor in parallel with the indicator bulb. That is there to provide field current to the alternator if the bulb burns out.
(A bit of useless information is that in Ramblers it was common for the charge light to illuminate dimly even when the alternator was working properly. This was due to variations in bulb manufacturing or the bulb being replaced with the wrong type.)
The alternator and the regulator are separate from each other.
That's confusing. So the regulator is not attached to the alternator, and your system doesn't match the diagram I posted?
Pictures would be great.
There is a connector and a stud that both hook up to the alternator.
One is a stud that hooks up to the orange/black cable
Since at least 1995 the regulator is part of the alternator on the Ford Ranger
Find that connector and disconnect it.
Find which connector? Fuse 15, or the 30-amp fuse?
I think he's talking about the connector on the alternator
Then, while you have that connector unplugged, check for power on the connector terminals that have the YLW/WHT wire going to it (should have power always)AND the LT GRN/RED wire (should have power in Run and Start).
I touched the yellow/white wire. The voltage drops to zero and is unsteady. It basically drops to 0. Is this normal? I don't think it is. Lol.
That's not normal. That yellow/white wire comes from the FM14 (30 amp) Generator Voltage Regulator Fuse in your underhood fuse box
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It's a high amp circuit and it sounds like you have some serious Voltage Drop going on here. If that wire can't support the current to the alternator then the alternator's internal voltage regulator won't turn on
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If you don't feel like tracing the circuit for the problem maybe try this setup. See how the guy cut the yellow/white wire and got a wire ring terminal and just wired that yellow/white wire to the B+ threaded stud on the alternator?
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If that works the only thing I'd do differently is get a waterproof inline fuse holder at the auto parts store and put a 30 amp fuse in that wire like the Ford engineers designed
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I fixed it around an hour ago. The 175 Amp mega fuse was bad. After we put another mega fuse in, it cured the whole thing. I've never heard of a mega fuse before. That was the original mega fuse. Thanks, I was really starting to pull my hair out. Electronics are not for me, lol.
That's a whopping big fuse! I'm used to seeing fusible links for protection of high-current circuits.
I know, it was almost a component all on its own, lol. It was only $6 for a new one.
mega fuses are new to me as well. My current vehicle has a fusible link in the cable from the alt to the battery , and then a 125A megafuse in the under-hood fuse block where power distribution branches to the cabin fuse box and to the rest of the body systems. I guess with all the electronics in newer vehicles, they needed additional protection with all the current passing through the firewall.
Anyway, glad you got it resolved Justin. Did you perform an autopsy on the fuse? Did the element just burn out from a short, or was some other kind of failure?
I think it just failed due to corrosion, corrosion increases resistance, as you know. I replaced the original mega fuse, so it had been in there since they built that truck almost 24 years ago. It's been in the salt for many years, so that's definitely a possibility.
It was a side thing. I knew where the main fuse box was located, but not the mega fuse. It was kinda buried and I assumed it was supposed to be like this. It's all plastic, and thought it might be to reinforce the box. I never expected there to be a fuse inside. There's no outward indication that the fuse is there.