My mother-in-law has asked me to fix her 1983 Ford F-150. I assumed it wouldn't be so bad, but I honestly don't know much about not only domestic vehicles, but old ones either.

The alternator had been replaced because the battery was not charging and that's where I've stepped in. With the alternator bolted in, but no wires connected. I think I've sorted out some of it.

This is a 1983 Ford F-150 with a 302 V8 & battery gauge in-dash.

1. When the key is turned, nothing happens. No crank or even clicks.
2. The truck will crank if I & S are jumped, but the starter will not stop.
3. Even if I & S are jumped, there is no spark unless the yellow wire (connected to nothing in the picture) is connected to I or S. If connected, it runs great.

The yellow wire exiting the top of the picture is connected to the ground terminal on the alternator. It goes into the connector and up into the loom. Meter says it's a ground.

The smaller orange wire exiting the top of the picture is connected to the field terminal on the alternator. It originates from the F on the voltage regulator.

The darker wire exiting the top of the picture is connected to the battery terminal on the alternator. It gets 12V from the positive side of the starter solenoid. Meter says it's +12V.

The green/red wire for S on the voltage regulator goes into the same connector as the large yellow wire and up into the loom.

There are two yellow wires coming from the I on the voltage regulator. One goes into the same connector as the battery wire and the other (shorter) goes to the I on the starter solenoid. Meter says it's +12V.

The red wire for S on the starter solenoid comes from the same connector as the large yellow wire. Meter says it's a ground.

What I cannot figure out for the life of me is:

1. Why does the ignition switch do nothing?
2. Where does the yellow wire go? (From question #3, above.)

Thank you for any time and help. This is a great truck when it's going,

 

Ok... I got somewhere. The large yellow wire at the top of the picture, if that's connected to +12V, everything in the cab works. Which I did not even notice before that the blower motor/stereo would not come on.

So it cranks with the key when that is connected to +12V and fires right up. (With a jump start.)

Should that go to the +12V battery terminal on back of the alternator along with the battery cable from the starter solenoid?

Also, the alternator still is not charging and the battery is registering -12V on the meter.

Thanks again.

 

The big fat yellow wire does feed all the electrical, and if it will reach, should go on the large stud on the starter solenoid(the one that goes to the battery). You are doing the same thing by hooking it to the bat lug on the alternator, but it should go up to the starter solenoid to get 12v there.

Once you do that, check to make sure you have 12v on the bat terminal of the alternator with the engine off. The wire going from the alt to the battery connection(it originally went to a splice in the harness) used to have a fusible link in it. If this burnt out, you won't get 12v down there, and the alternator can't send the charge to the battery.

P.S. I just thought more about it, and since the cab had power when the large yellow was on the back of the alternator, then the alternator output wire is probably good.

 

Ok.. So here I am nearly a year later and this thing is still not charging. It starts right up and sits at 12.5V...

New voltage regulator, new alternator, questionable battery but same results with any battery. The A terminal on the voltage regulator above is going into a fusible link and to the Bat terminal on the alternator. Shows 12V.

The S terminal on the voltage regulator goes into the harness and I imagine to the ignition.

The F terminal on the voltage regulator goes to the Field on the alternator.

The Bat terminal on the alternator goes to a fusible link, one wire coming out of the fusible link goes to 12V side of the starter solenoid and from that, to the battery. Another wire coming off the fusible link is red and goes off into the harness. The last wire on the fusible link is to the voltage regulator's A terminal, above.

I get 12V at the alternator's Bat terminal and also 12V at the voltage regulator's A terminal.

Could someone point me in the right direction? I have checked diagrams, double and triple checked wiring. I have bought another new alternator, another voltage regulator and still nothing. It would be very handy to have this thing running around here.

Thanks again.

 

Take your meter and put it on the "S" terminal of the regulator. When you turn the keyswitch to run you should get 12v there.

If you don't and want to do a test, take a jumper wire, go from the battery + to the "S" terminal on the regulator, and then start the engine and see if it charges. If it does it verifies that the "S" terminal is your problem, it should be coming from the keyswitch circuit, and should have 12v with it on, nothing with it off. It's what brings the alternator and regulator "online" to get ready to charge, and takes them "offline" so they will not run the battery down with the key off.

 

Yep, getting 12V there, too.. Maybe I will go get this alternator and voltage regulators tested tomorrow and see if they check out. Should.. Both new.

Thanks again.

 

If you want to test the alternator yourself, take the field wire off the back of the alternator and tape the end so it doesn't short out. Then take a short piece of wire and hook it to the f terminal on the back of the alternator, and lay it up near the battery. Start the engine. Measure the battery voltage, and then touch the field wire to the battery +. The alternator should go wide open, you will probably hear it, and the voltage should jump way up on the battery, probably 14v +. That will tell you if the alternator is good.

 

I did that today and the alternator did go wide open, up to around 16V. Would it be the voltage regulator? I unhooked the field and noticed that it would start to stumble and die. Then I hooked the field back up and the alternator kicked on and took it back up to 12.5V.

Also when I did that, the ground wire to the alternator melted the shielding.

 

The engine should run off the battery. It should not stumble and die if the alternator is not working. You have a wiring problem somewhere. I would take the large alternator wire and unwrap it out of the harness. Make sure it's connected to the battery + in some form or fashion. Look for corroded wires along the way.

 

Well, it works.

Thank you very much, Franklin2 for helping me. If you notice, it's been over a year. The battery that was in it was bad at this point and it was out of gas.. Which is why it stumbled and died.

It runs great and runs at 12.5V.. I don't know how true this is, but a friend told me that the older externally regulated alternators in these trucks run at 12.5V, not 14.5V. Which is how it's acting, it does not let the battery drop below 12V, once it gets close, the alternator kicks on and takes it back up.

That's fine with me, it's an old farm truck that might have to power the lights and that's about it.

Thanks again, Franklin2.

 

12.5 is really not high enough. But if it works, ok. There can be some variation in meters. I wonder what your meter reads on the battery with the headlights on.

The lowest I have ever seen a older charging system run was around 13.5v.