i have a suspected problem with the voltage regulator on my alternator, but the problem is intermittent. so each time i've brought in the alternator to get tested at checker, it passes their test, so they won't replace the alternator (it's an autolite and has a warranty). are there any ways to get the alternator to fail, or at least ensure the problem will be reproduced when they test it?

at random times the voltage needle on my truck will start bouncing then go to the left and the battery light will come on. then after a period of time (15 minutes to 2 hrs) the needle will go back to the middle and the light will turn off. with the alternator on my truck the guy said it wasn't charging at all, but the alternator on their machine inside says PASS.

any ideas? thanks.

-jason

 

If you want to make it fail, over load it. Put in a dead battery, and try to get the alt to charge it up. That is a pretty good load, and I've read that it is NOT recommended to re-charge a dead battery using only the alternator.
That being said, why not get a real ammeter and put it between the alternator and the load side on the solenoid. Most, if not all, of the load on the system when it is running is carried from the solenoid to the fuse box, and you can isolate that load and pass it through an ammeter. If the meter shows flow from the battery to the load, the alternator is not supplying the necessary voltage/current. If the flow is from the alternator to the battery, the alternator is keeping up.
The voltmeter is an indicator of the load on the battery and how well the alternator is keeping up with the load. It should read about 12.6 volts on a charged battery. If less, the battery is low on charge, or the load is more than the alternator can produce. Your needle flickering around is a possible result of a bad voltage regulator on the backside of the gauge panel, or a loose connection on same.
I would check the engine ground, the wire from the alternator to the battery or solenoid(or fuse box) and look for bad connections there, too. Get a voltmeter or DMM, and check the real voltage when the needle is goofing around.
tom

 

Is there any sign that there is a problem other than the instrument panel? The next time this happens, pop the hood with the engine running and use a multimeter to measure the battery voltage. I'm more suspicious of the gauge acting up than the charging system actually having a problem.

tomw - maybe you can fill me in a little more, but are you sure that's a good idea to put an ammeter in series with the alternator? A lot of the run-of-the-mill multimeters are fused at 10 amps. Even my Fluke is fused at 10 amps. Even at idle, the load on the system is pretty heavy. The coil alone can draw that much. Are you saying that only a fraction of that sources from the alternator? I'm not claiming you're incorrect; I'm asking for more information. I've never really investigated how much current comes from the battery, and how much comes from the alternator.

 

yes, there is other indication. i first brought my truck in to get the alternator tested and the guy at checker tested it and said that the alternator wasn't charging at all. then when i brought just the alternator back, it passed there test in the shop.

 

Only one way to find out and that's measuring the battery voltage while it's running.

 

fmc, I meant a real ammeter. Either the one that is put in series or one that you can hold up to the wire for measurement. A DMM will only carry so many amps before it blows the fuse or melts the gizzards. I have a trio gauge set on my workbench I had planned on putting in my Ranger that includes an ammeter. It would require that all charging amps and load amps in excess of alternator output be carried to the back of the meter to indicate charge or discharge and the on to the battery. That is why the beancounters went to voltmeters as they only require the voltage not the amperage be available at the meter - smaller wire and less chance of a 'meltdown'.
When you install an ammeter, you basically put the meter in series with the load, not starter, on the battery. That is why you can 'separate' the load from the starter at the starter solenoid in most cases. If the alt is working, you will see a near zero reading. When the battery is charging after startup, you will see the charge amps. When the alt is not up to the load, you will see discharge to run the load.
tom

 

does anyone have a ford part # for the alternator wiring harness? the harness says F6TB 14305 P260H. but i can't find that online anywhere


97 F250 HD 460