I'm kinda suspicious of the wiring on my alternator. I got a new batter a couple months ago and haven't driven the truck since. I tried to start it and it will not start at all, no clicking interior lights, etc. I had the alternator checked and it checked good. I replaced the voltage regulator the same time I changed the batter because it went out. My system was overcharging and blowing all my lights out. I tried to jump the truck and it jumps just fine but when I pull the jumper cables off, the truck dies. I suspect the alternator is wired wrong and not charging the battery. Can anyone confirm the wiring on my alternator? This view is with the adjuster bolt removed and alternator rotated and resting against the passenger side firewall. Thanks.

-Destin

 

If the truck is completely dead and you don't even have interior lights, that sounds like blown fusible links.

It's hard to comment on your wiring because the picture doesn't show the post designations on the back of your alternator (FLD, STA, BAT) etc. You need to trace where they go against a wiring diagram using the wire colors.

 

The truck will start and run fine with a new battery. I'll look on the alternator and see if there is any designations for each post. I vaguely remember seeing something. What are the fusible links?

-Destin

 

If the truck runs fine with a new battery, nevermind the fusible links. They are these inline one-time fuses at the very start of your vehicle's electrical system, near the stater solenoid.

 

Here is a backside picture with the post designations. I guess the only thing to do would be unwrap the harness and see where the wires go? Obviously battery to bat and ground to grd, but what is the FLD and STA posts? Thanks for the input fmc400, you've been a help in the past.

-Destin

 

Right so far. BAT goes to the battery, and the A+ terminal of the regulator ties off this as well. FLD goes to the F terminal of the regulator. When the regulator wants the alternator to output current, it turns on the F terminal and creates a field excitation current (hence the abbreviation FLD). This creates a magnetic field, the moving rotor results in a changing flux, which creates a voltage, yadda yadda yadda. STA stands for stator. If your truck has an ALT light, then this terminal goes to the S post of the regulator. It's what tells the regulator that the alternator is turning, and brings the regulator online. If you have an ammeter gauge on the dash, then I don't think it goes to the regulator. On both setups, another line ties off the STA terminal and goes to the electric choke.

 

Opened up the wire harness and this is what I found.

Black wire to Battery with (a) regulator wire tied in. There are 2 yellow wires that come from the (a) part of the regulator. One wire goes to a little metal piece that is grounded to the regulator mount bolt.

Orange wire to Voltage Regulator (f).

White wire runs through the harness and into the cab where I can't see. I assume it's suppose to be grounded somewhere. It goes into a 2 wire plug right at the voltage regulator. The green wire on the plug comes out of the voltage regulator (s) and inside the cab. The white wire goes from the alternator through the plug and inside the cab. I'm using a wiring diagram in my Haynes manual but it's a little different than whats on the truck. Also the Haynes manual doesn't say anything about a ground. Can I just run a wire from the gnd on the alternator to the chassis?

-Destin

 

Of the two yellow wires coming from the A terminal of the regulator - the little metal piece should be the noise supression capacitor. The yellow wire shouldn't ground directly; it should connect to the capacitor (also sometimes called a condensor), which itself grounds, usually through the regulator mounting bolt.

Your orange wire should go from FLD on the alternator to F on the regulator.

The white wire might be hooked up incorrectly. I notice your stator (STA) is left unconnected. I need to know more information - does this truck have an ammeter gauge or an ALT light? Do you have an electric choke?

As for the ground, simply bolting the alternator to the engine block should do the trick.

 

In addition to my post above - I notice your BAT connection on the alternator isn't insulated. From the factory, it would have had a rubber boot to shield the connection. Over time it falls off or is broken off. It's not a good idea to have an exposed 12 volts so close to so many grounded conductors.

 

I don't have an alt light on the dash and I do have an electric choke. I'll get a cap from the parts store for the battery connection. Thanks.

-Destin

 

Sorry, I overlooked the obvious. I have an alternator gauge and it does work, so that would be the white wire? I just looked for an alternator light.

-Destin

 

My understanding is that if you have an ammeter gauge, then the only thing drawn from the STA post of the alternator is the electric choke. If someone can verify this with a factory wiring diagram, that'd be wonderful. I'm curious if the white wire in your picture is connected incorrectly and is actually for the electric choke; it doesn't make sense to me that it'd be the ground wire. If it was a ground wire, it wouldn't be that thin of gauge, and wouldn't run up into the cab.

 

So I would think that the white wire would go to the sta on the alternator and I just need to make up a ground wire? The Haynes manual says that the white wire should go to the (s) tab on the regulator and that's not the case. I have a green wire that comes out of the (s) tab and runs into the cab. The Haynes manual also says there should be a red wire that comes out of the I tab from the regulator to an alternator indicator, which I don't have a wire on the I tab at all.

-Destin

 

I believe the alternator indiciator is for the ALT light setup. The standard equipment on these trucks was an ALT light that comes on if the alternator doesn't turn, and optional equipment was an ammeter gauge. The wiring between the two setups is completely different. Unfortunately I do not have schematics for the gauge setup, so I can't be of much help there. I hate to pass the buck, but if no one chimes in with the wiring diagram you need in the next couple days, I'd post this question in the electrical forum. Franklin2 over there will definitely have them.

I don't have a ground wire on my alternator, because it grounds by bolting to the engine block.

 

I went to Napa to see if they could shed any light on the wiring for this alternator and they told me it was the wrong alternator for this truck. It may be, but it starts and runs. This alternator is a rebuilt Motorcraft 75 amp and the one they tried to sell me was a 61 amp Motorcraft. Anyways they couldn't help me with the wiring so I put the battery cable to bat, orange wire to Fld, and the white wire to Sta. First time it's been started in 3 months and it fired up after about 3 seconds. I put the battery from my jeep in it to start it up and the voltage on the battery prior to starting the truck was 12.6v. After I started it, it dropped to 12.2v and after a couple minutes it came up to 12.3v and stayed there for about 20 minutes. I suspect if there was a charging issue the voltage would have dropped after running for 20 minutes.

Update: Just checked the voltage on the battery after shutting it off 10 minutes ago and the battery reads 12.6volts. Why would it have gone back up.


-Destin