Thanks in advance for help with this.

I've got a charging issue, and I'm really good at electricity. My 1986 2.9 recently had an alternator go bad. Had the good old lifetime O'Reilly; they gave me another. That one didn't charge. They gave me another, but one didn't work and tested bad on their bench test. Got another. Didn't even try to put that one in as something was hanging up when I spun the pulley. Waited a day and got another. Tested ok on the bench, or so the kid said.

After installation, I pulled off the pos cable and the engine died.

I went through something like this a year and change ago; got two bad alternators from Rock Auto, and it was the O'Reilly alternator at that time that gave me a year. I went through a lot of wiring checking a year ago. Should I consider a fusible link problem...? What fuse might control this? Or...? I don't know. The issue from a year back was getting a good alternator. I don't know where to start here after all of this.

Any help or advice would help.

Thanks,

Tony

 

1986 should have voltage regulator built into the alternator, does it?

If so test voltage on the B+ wires on the stud terminal on back of alternator, they should read Battery Voltage, i.e. 12.3v-12.8v, don't need to disconnect to test these wires
If not then yes fusible link is bad

There is also a Yellow wire on the alternator, it should also have Batter Voltage, uses same fusible link as B+ wires, disconnect to test this wires voltage

And there is a Light Green wire on alternator, it comes from ignition switch, this is the ON/OFF power for alternator, disconnect to test, should ONLY have 12volts with Key on, 0 volts key off
An alternator doesn't generate any voltage simply by spinning it
It must have "startup voltage" to power the rotor and THEN it can generate its own power, the Light Green wire provides the Startup voltage

If light green wire had 12volts key off then alternator would act like an electric motor, and try to turn the engine via the fan belt, lol, so battery would drain pretty fast, so ON/OFF switch for alternator
On later models this wire is also the Battery Light


The Fusible links all terminate on the Starter Relay post that has the Positive Battery Cable connected to it
There are a few of them
Alternator uses 16gauge (often Orange color) fusible link, but there can be more than one 16gauge fusible link in 1986 Ranger

 

Ron,

Thanks so much; very concise and helpful.

This 2.9 has always had the offset mount alternator, with a v-belt pulley. No stud or wire on the back side of the alternator. Yes on the built-in regulator with the yellow wire and green wire. The two stator wires are fused into one, and this loom of three meets at a connector by the steering wheel. I'll do those tests. A little weirded out about the stud thing; I've had this truck for fifteen years, and this is its third alternator. The first way back lasted for ten years. If anything there sounds strange, I'll sure listen to your directions. Oh, on the fusable links by what I've always called the solenoid, those are 15 amp?

As always, thanks so much.

tony

 

Fusible links are usually 60-70 amp, whatever the alternators rating was, they are like a "slow-blow" fuse, they can take a spike in amps without blowing, like during start up

Test the two fused wires, they should have battery voltage, all the time

As should the yellow wire, they share the same Fusible link

Green wire, 12v key on only

Yes, they "don't make 'em like they used to"
So new alternators won't last as long


Starter Relay on the inner fender was also called the starter solenoid by many people, but it is a relay

All the fusible links will be on the larger post with the Battery cable, this is the main power distribution for the whole vehicle

They look like this:
It's just a short wire with a non-flammable metallic wire and insulation, so it will melt if over heated(a short) and separate(blow) without causing a fire

Some have the rubber tab some do not, most Ford links will have it and and "eye" on one end, the other ends connector can corrode and cause a bad connection

 

Thanks for that Ron, and all of your help. I've done the voltage tests on the yellow and green wires. They read the same as the battery voltage. It's gotta be another bad alternator. I went back to O'Reilly and they have another one coming in... I think the guy said it was coming from back easy.

Just to be safe, I ordered a back-up on Amazon. I can't have the truck down, so it's over-the-top solutions at this point.

I really appreciate the info on these fusible links. I learn a lot from your help.

Tony

 

Its fairly easy to switch over to a 3G Alternator, which will last longer and have more AMPs

You need to run new B+ wires(bigger gauge for the higher AMPs), with fusible links(or MEGA fuse), but the current yellow wire and green wire can be used

Most 3G alternators will have serpentine belt pulley so you would need to swap that over for your V-belt

1G = 1st generation
2G = 2nd generation
ect..........

How-to here: 3G Conversion - Gary's Garagemahal (the Bullnose bible)

Yes the yellow wire can just be hooked up to the B+ alternator terminal, even on your 2G

 

Hey Ron,

Thanks so much; I will definitely check that out, great suggestion.

Well, I've got the O'Reilly alternator in the truck, and am charging the battery. Thinking ahead... can you give me a short heads-up on how this circuit flows. If this one is bad too, then I have to consider that something along the line may be messed up. I assume the charging circuit goes through the ammeter gauge, and returns through one of those fusible links on the starter relay?

Thanks again,

Tony

 

No on the Amp Meter

The amp meter is connected at 2 places on the larger "fused" wires that run from alternator to Starter relay post
It only reads about 5% of the amps and its a DIRECTIONAL flow meter
i.e. are amps flowing toward the battery(+, charging) or toward the alternator(-, not charging)

Running the full 65 amp alternator output thru the firewall and thru an amp meter in the dash would be dangerous, it would also require battery cable size wires

You could connect amp meters 2 wires to alternators B+ and starter relay post, it doesn't matter as long as they are separated by a few inches, 6 inches at least, and are in correct direction.
But its safer to have amp meters 2 wires between fusible link and alternator for protection

i.e. if you hook up the 2 amp meter wires and start the engine, and battery voltage shows 14+ volts(alternator is working) but Amp Meter shows -, discharge, then wires are reversed, swap them around and Amp Meter will show +, charging.

Electricity/amps, travel on the path of least resistance, so the smaller amp meter wires is a harder path than the larger B+ wires, so majority of amps travel on the larger wires, and that's why the amp meter wires should be protected by the fusible link, if B+ wire failed ALL the amps would try to flow thru the amp meters smaller wires, which would burn out the wires and amp meter, and this DID HAPPEN, which is why you don't see Amp meters any more, lol

.................................................. ./-------amp meter----------\
Starter relay----------(fusible link)/---(amp meter shunt)-------\-------------------Field(B+, alternator)

The part of the wire between the 2 amp meter connections is called the "amp meter shunt", its not a special wire, its just what its called



Alternators work like this:
If you spin an alternator it will never produce any voltage, 0, nada, zippo

You must supply it "start up voltage" first, this is what the green wire is for, green wire is hooked to voltage regulator
The voltage regulator applies voltage to the ROTOR, the part that spins, usually about 9volts is max
This creates a magnetic field around the rotor
In the Case of the alternator are 3 Field Coils, each Field Coil has 2 Diodes
As the Rotor is spun by the engine the spinning magnetic field causes AC voltage to build up in the 3 Field Coils, the 2 diodes convert AC volts to DC volts
The 3 field coils DC volts are combined and sent out on the Field/B+ connection to the Battery positive cable, this connection must be fused.

The Yellow wire is connected to the Voltage regulator, and battery positive, it measures "electrical push back", my term
In any electrical circuit when you turn it on the there is an electrical draw, then a "push back" when system is fully powered up, draw is there but less

Voltage regulator uses "push back" to set Rotor voltage, 7 to 9volts usually.
After start up the battery is drained from starter motor use, so low push back and voltage regulator sends rotor 9 volts for full charging, usually 14.5volts to 14.9volts
As battery gets recharged it starts to push back and voltage regulator starts to lower rotor voltage.

Target voltage is 13.5volts, under 14volts for sure, as over 14volt long term will "cook" a 12volt battery.
1 volt above "battery voltage" is what you should expect after engine has been running for 5 minutes or so
So if battery voltage is 12.6v key off then expect 13.6v after 5 minutes

When you turn on headlights push back will drop until lights are powered up so voltage regulator will see that and increase rotor voltage, same for heater blower on HIGH, push back drops so regulator increases voltage to rotor

Alternator generates more voltage at higher RPMs, so regulator lowers voltage to rotor as RPMs increase to maintain the 13.5volts

If voltage goes up and down with RPMs it usually means voltage regulator is bad, stuck at a fixed voltage to rotor, if its stuck at 9volts then it will cook you battery with 14+ volts

If headlights dim at idle(no thats NOT normal, lol) that usually means 1 of the 3 Fields has failed, so alternator can't produce 13.5volts at low RPMs


So Field/B+ wire is connected directly to battery positive, as is the Yellow wire, both should be protected with a fuse or fusible link
Flow is to the battery when alternator is working

Green wire is used for start up voltage so flow is from ignition switch to the alternator/voltage regulator, this is also Battery Light circuit on newer vehicles
If green wire had power all the time(key off) the battery would drain pretty fast

ONE WIRE ALTERNATORS
You could use one of these since you have an amp meter
These use an RPM switch instead of the Green wire
They just have the ONE larger gauge wire connected to battery positive, with a MEGA fuse.
When you start the engine and RPMs are above say 600 the internal switch closes and sends 12v from B+ post to the voltage regulator
Yellow wire is not needed because voltage regulator is connected to B+ as well for push back

Down side for these on newer vehicles is no battery light, but you can add a voltage gauge, digital
Also the RPM switch can fail and either cause no charging OR it stays closed and battery drains so no start

 

Ron, thanks for that great tutorial. I sure appreciate the time you put into that.

Well, dunno yet if this thing's gonna work. I don't have a B+ stud on this alternator, so I will have to read through this and see what kind of output test will work here. Probably a mickey mouse deal to pop off a cable and see if the idle holds. My wife just called and wants some help in her pet sitting biz, so I will return to this and report back.

tony

 

The 2 Larger wires are on the B+ terminal, its the "output" voltage of the alternator and is hooked to Battery Positive via Mega Fuse or Fusible link, so this wire should have 12v all the time, if fuse is OK, and battery cable is hooked up, lol

Same for Yellow wire, 12volts all the time, if not fuse is blown

Green wire, is key on 12volts, 0 volts key off

If all these are OK then vehicle wiring is good

If not charging after start up then alternator is bad

Its really a simple system

Only other issue can be the GROUND, Battery negative cable needs good connection to engine, so alternator has a good ground to complete the circuit
1986 2G alternator may have its own ground wire, it needs to be same size as B+ wires usually

 

Ron,

Thanks for all of your help, and the detail. It seems that the alternator I purchased from Amazon is charging. O'Reilly gave me four bad ones. Unbelievable. I learned much here, and it's appreciated.

Tony

 

Thanks for the update

We are the Quality control now, so non-OEM parts are not tested, just boxed and shipped, 4 bad ones is not common but 2 of the same brand not working wouldn't surprise me
People run into that with fuel pumps quite often, Motorcraft are like $500, 3rd party $150, but you often have to install 3 to get one that lasts out the 1 or 2 year warranty

 

Wow, that's what got me going with this problem. I figured it would have to be some funky wiring under the dash, not four bad alternator in a row!

Oh, Ron, btw, I'm checking out the threads for an idle issue... My idle starts out fine, but gets a little funky later. I've replaced IAC, MAP, and TPS. No, connectors aren't replaced. Checking through the threads to see if anything relates.

Thanks, as always.

tony

 

So cold engine idle OK, then poor idle after full warm up?

OR

Cold or warm startup idles OK, after a few minutes idle is poor?

 

Hey Ron,

Definitely better at cold.

Was just out there; it hadn't cooled down completely from the day's business. I pulled off the MAP sensor connector, the IAC connector, checked vacuum lines from underneath plenum, from the EGR, to the charcoal canister. Nothing obvious. Was thinking that I might have a bad power brake vacuum booster, but did a street test of pumping the brake five times, then started up the engine and the pedal went down a half-inch or so.
We're slammed in the pet sitting business through next Tuesday, so I can look at it on the fly. My first thought is to check the plugs and see if some gas cleaner helps, (fuel filter is 6K old).

The big deal that I've noticed is it wants to die after I cruise up a hell and come to a stop.

Scratching my head here...

tony