1996 F53 alternator has no output

[MarvinG]

Update (typed following before seeing subford’s update): I do have voltage on the I circuit after all. Apparently my test probe wasn’t getting in far enough to measure previously. I talked with the tech support for the alternator and his suggestion after going through the tests with me, is to take the battery in and make sure it is good. (It shows 12.36 volts now after sitting with terminals disconnected for a couple of days. I’ve charged over 24 hours with a 6-amp charger and the settled voltage was 12. 7 after charging but specific gravity in the cells was on the low side of fair.) Once I have a known good battery, if the alternator doesn’t charge, then we may be down to TJay’s comment about needing to obtain two alternators before I get one that works. . . . Case is still open, will update again soon. Thanks for all the help so far, I will save the diagrams you’ve posted subford for future use if not needed now. They are a big help. I’m listening if further thoughts in the mean time.

[MarvinG]

Battery tests good, old alternator tests good. . . . . Hmmmmmm.

[MarvinG]

I put the original alternator back on, it is a rebuilt motorcraft sold by OReilly. Two shops tested it and pronounced it good. Still no output. I rechecked voltage on the I circuit and with the plug connected to alternator, I only get 2.65 volts. I unplugged the connector where Subford suggested and get battery voltage coming in. I then started engine and jumpered the outgoing wire to the alternator to battery voltage with no change. Still no output.

I notice battery voltage of about 12.37 at the battery and at the alternator terminal. However, when I start the engine, battery voltage drops to 12.05 and at the alternator and elsewhere drops to 11.9. Is that what I should see? If not does it point to anything specific?

I am really bumfuzzled on this one!

[subford]

Originally Posted by MarvinG

I then started engine and jumpered the outgoing wire to the alternator to battery voltage with no change. Still no output.

Please explain what you did.


Did you put a wire from the B+ on the alternator to the disconnected C407 going to the alternator?
If so and no output it sounds like you have an open fuse link.

[MarvinG]

No, I actually jumped from the B+ On the starter relay which is right beside C407. When I jumped it I had 11.9 volts there at that terminal and also measured 11.9 volts at the I connection on the alternator (when jumpered.)

[MarvinG]

I suppose the next logical thing to do is to put a pigtail on the alternator output and connect battery jumper cables up and see what I get. Though I can’t for the life of me find a logical reason this isn’t working.

I am about to lose interest in this project! However, we are just now approaching the time of year I like to camp, so I’m not yet ready to call a junkyard to come get it.

[Greg20d]

I had a issue very close to what you are describing and I found a loose wire on the battery ,,, but it would not start etc,

[MarvinG]

Right, Friday mine wouldn’t start and I found the same, unfortunately, that didn’t solve my charging problem. I think the loose wire in this case was the result of my continued connecting and disconnecting, and probing around among, the battery cables. This morning I’m going to connect directly to the battery using jumper cables, but first I’m going to bypass whatever is causing the voltage drop I find. I suspect the battery disconnect (that some call the salesman switch.)

[subford]

Deleted, deleted.
Posted in the wrong Thread.

[MarvinG]

The alternator B+ does not go through the battery cutoff switch. Nevertheless, I’ve bypassed the cutoff switch completely, I’ve run the B+ directly to the battery with battery jumper cables. No charging. When this problem originally began, the alternator light was not on, but the alternator just wasn’t keeping up with demand. Now the alternator light stays on and no output at all. About the only thing not bypassed or tested is the #4 wire from the regulator to the stator and the plugs connecting to the alternator themselves. The wire looks OK as do the plugs but I am running out of things to check.

[subford]

You might try running a jumper cable between the NEG terminal of the battery and the frame of the alternator housing.
The alternator may not be grounded.



Leave your other cable jumper cable between the B+ terminal of the alternator and the battery POS terminal.


Make sure the "A" wire #36 is also has battery voltage on it also along with the "I" terminal.

[MarvinG]

When I ran the alternator B+ via battery jumper to the battery, I also grounded the alternator the same way. I didn’t test the A wire today but it had voltage last week when I tested. I am out of ideas, I don’t know what a professional mechanic would do that I haven’t already done.

[MarvinG]

Probable cause of the problem. This is the plug on the alternator (#4 wire going from voltage regulator plug to this plug going to stator on alternator.) The wire coming out of plug is burned in two and the metal connection part of the plug looks like it has been hot. I will cobble a connection in the morning to prove it works then find a new or used plug assembly to replace.

[MarvinG]

Update: installed new plug. Unfortunately, the alternator light stays on and no output. I’m taking the Autozone alternator into town tomorrow to get it checked. Perhaps I damaged both alternators someway while testing before I found this bad plug on connector.