My 1976 Ford tractor had a complete wire harness meltdown. I untaped the harness and can see the large diameter wire from the alternator to the Ammeter and then on to the battery got REALLY HOT. Ultimately the insulation melted off, gave the unit a hard ground and then burnt the wire in two.
I can't see the initial cause. One possible is the alternator stuck on full amps. So, how can I check if the alternator and separate regulator are good?
Karl
I'd suggest that it's not worth the effort. Just replace the old alternator and regulator with a modern "one wire" alternator and be done with it. I did similar on my old Deere backhoe to replace an old POS Motorola alternator and regulator.
It seems more likely that the connection shorted to ground and the current flowed from battery to alternator. If so you may find the alternator still shorted, or you may see signs on the connection between alternator and wire.
I think that an alternator repair shop should be able to check this for you if you bring the parts in. Absent that you should be able to check the regulator operation if you have a variable-voltage supply -- but do you have such a well stocked electronics bench?
What? And ruin the value of his tractor as an untouched antique? Do that and some restorer will be seriously torqued 50 years from now.
Karl: bury it in a concrete-lined pit filled with desiccant, for future generations. Then go by some new Japanese thing.
Output from an alternator depends on rpm and excition. A repair shop would test the alternator by running it at low speed and substituting a rheostat for the regulator in order to have manual control over the excition and gradually increasing rpm and excition until rated output was reached or something got hot.
If the wire from the alternator to the battery was correctly sized for the alternator it is doubtful if the alternator could have put out so much amperage as to overheat the wire. However, if one or more of the diodes in the alternator had shorted the battery could have been connected directly to ground through the alternator case and in that case the battery certainly could have put out enough current to damage the wire.
I would suggest checking the diodes in the alternator first.
Cheers,
Bruce (bruceinbangkokatgmaildotcom)
Would this check do it:
put temp wire from battery to alternator ouput with a fuse. if fuse don't blow, this is OK.
The alternator shop is 45 miles away, I'll be trying to reconnect without making the trip. I just want to be sure i don't remelt the wring. if the alternator/regulator don't charge right, I'll replace with a GM Delco type.
Karl
Blown diode or shorted out wire in the loom somewhere.
First off, hand the alternator to your local auto parts place, they can do a free check > My 1976 Ford tractor had a complete wire harness meltdown. I untaped the
Karl If this is a Motorcraft alternator. Start the tractor and with a voltmeter on the output of the alternator check the output voltage. If it doesn't go over 15 with a charged battery you don't have a problem. If it doesn't charge, full field the alternator for a few seconds by applying 12 volts to the F terminal. If it charges then it is most likely the regulator that is the problem. I am thinking in order for the output wire to melt the amp gauge may have shorted out so you might want to bypass it temporarily. I don't think I have ever seen an alternator problem that would melt the wire going to the amp gauge or battery. I would think it would just cook the battery. Steve
The "Dead short" depends on your meter -- most of my DVMs don't show diodes as all the way short, and IIRC you should see the armature winding resistance as well.
But it should certainly show as open in the other direction.
OK, So the terminal is marked FLD instead of F. Take a peek at one when you have a chance.
If this is an ALTERNATOR, not a GENERATOR, it is unlikely to have an "F" terminal....
My vote is for a shorted diode or something contacted the terminals on the ammeter, and the current was coming from the battery.
And through all the mergers and acquisitions, Prestolite owns Motorcraft and Leece-Neville and Motorola alternators. You really need to write Prestolite and ask what to replace it with, they are re-numbering everything and making one system - slowly...
There is supposed to be a large fuse or a Fusible Link at the battery terminals to stop this - the fusible link wire is special composition with tin in the mix so it heats up and melts open easily, has higher tempo insulation (silicone) to contain the melty bits, and one or two gauge sizes smaller than the wire it protects.
You have to use a special barrel crimp without a center bump to splice the link to the protected wire, so there is a full overlap the whole barrel. Otherwise the current gets too concentrated and it blows at the splice.
Myself, I'd build a high current fuseholder and use the forklift battery fuses - they come in sizes from 100A to 400A, and mount to two studs.
And also fuse/breaker/fusible link where the other tractor main circuits tap off at the ammeter. If someone beefed up the electrical system to add a lot of night lighting or hook up a big inverter, they may not have followed proper practices to do it.
Doesn't matter if there is a fuse block for them, you need to protect the main leads heading to the fuseblock - Stuff Happens.
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I would first check your ammeter for shorts to ground. I have seen many of those ammeters short out and melt the wires since the wires are not fused. The terminal studs have an isulating bushing that keeps the stud from touching the metal case. These may not be doing their job and are allowing the stud to be grounded to the case of the ampmeter.
John
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