Testing the alternator
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Testing the alternator
It started working intermittently a few weeks ago... sometimes it would charge, sometimes it wouldn't... the more time passed, the more it leaned to the side of "not working". Now it hasn't been working for a few days in a row, and since I was still using the truck (starting/stopping), I obviously got stranded with my batteries too weak to start. (Which I expected, as part of my troubleshooting, and I was prepared for this.)
Now, the wires near my alternator have been spliced, and generally messed with, by some previous owner. There are connections taped with old electrical tape, so I suspect that might simply be the problem.
Can anyone help me with the wiring, which plug is what, etc.? Between which pins should I be checking for voltage with my multimeter?
I've looked for old threads (ideally with pics) and didn't find anything...
Thanks in advance!
Truck = 1994 7.3 IDI turbo (just in case the alts aren't all the same 83-94)
Now, the wires near my alternator have been spliced, and generally messed with, by some previous owner. There are connections taped with old electrical tape, so I suspect that might simply be the problem.
Can anyone help me with the wiring, which plug is what, etc.? Between which pins should I be checking for voltage with my multimeter?
I've looked for old threads (ideally with pics) and didn't find anything...
Thanks in advance!
Truck = 1994 7.3 IDI turbo (just in case the alts aren't all the same 83-94)
Lead Driver
Joined: Mar 2006
Posts: 5,096
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From: western SD
The large pin with the nut on the back of the alternater should read the same as the battery voltage. With the engine not running, and the batterys fully charged, the voltage should read above 12.5 volts. The same pin with engine running should be 14.5 volts, if the alt. is charging good.
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Let's say the voltage there is the same whether the engine is running or not... does that automatically mean my alternator is dead and must be replaced? Or could it be a faulty electrical connection somewhere?
Postmaster
Joined: Feb 2011
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likely you have a bad wire somewhere in that mess. does your truck have a 3g alternator or an old-style unit?
the alternator that came in my 87 had the twin output wires on that push-in connector, and a 3-position connector for the small wires.
the 3g in there now has the stud on the back for the output wire, and a 3-pin connector with a 1-pin next to it.
in both cases, the 3 pin connector has the pins labeled A S I, in which A is always hot (battery voltage), S on the 3g goes to the 1 pin connector next to it, but on the old models went to a switched hot line. I on the 3g went to the indicator light, and on the old model was not used. the indicator light should have switched power to its other side, and is usually powered with the gages.
i suspect the previous wiring job was done with all wires going to the right places, but no telling if they used proper connectors or played the horrible twist-and-tape game that i so often see.
if you don't like troubleshooting wires, you could just pull out the alternator, bring it to your local parts store, and have them test it for you. then you'll know for sure you have a good alternator if/when you start chasing wire
the alternator that came in my 87 had the twin output wires on that push-in connector, and a 3-position connector for the small wires.
the 3g in there now has the stud on the back for the output wire, and a 3-pin connector with a 1-pin next to it.
in both cases, the 3 pin connector has the pins labeled A S I, in which A is always hot (battery voltage), S on the 3g goes to the 1 pin connector next to it, but on the old models went to a switched hot line. I on the 3g went to the indicator light, and on the old model was not used. the indicator light should have switched power to its other side, and is usually powered with the gages.
i suspect the previous wiring job was done with all wires going to the right places, but no telling if they used proper connectors or played the horrible twist-and-tape game that i so often see.
if you don't like troubleshooting wires, you could just pull out the alternator, bring it to your local parts store, and have them test it for you. then you'll know for sure you have a good alternator if/when you start chasing wire
Fleet Mechanic
Joined: Jun 2009
Posts: 1,320
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From: CT
Most of the time the regulator goes bad on the 1g. The windings usually don't fail. I replaced the regulator, and the belt (not sure why but it helped fix it ), and no more charging light and i get 14.7 volts out of the thing.
Though i think you have the 3g since you have the serpentine setup.
Though i think you have the 3g since you have the serpentine setup.
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I have no idea what a 3g is nor what's a 1g, but it has the stud on the back for the output wire, and a 3-pin connector (from memory, green, white, brown) with a 1-pin next to it (which is white, and connected to the 3-pin plug).
That's a 3g?
Thanks all for the advice.
One thing is for sure, the previous wiring job WAS done with all wires going to the right places, as I've been driving the truck for two years now... and this problem started creeping in progressively lately, so it definitely is something going bad worsening over time, not in a binary way.
That's a 3g?
One thing is for sure, the previous wiring job WAS done with all wires going to the right places, as I've been driving the truck for two years now... and this problem started creeping in progressively lately, so it definitely is something going bad worsening over time, not in a binary way.
Lead Driver
Joined: Mar 2006
Posts: 5,096
Likes: 1,498
From: western SD
A fully charged battery should read 12.5-13 volts with engine off. If your voltage reads 12.75 with engine off, and the bolt in the back of the alt. reads the same with engine running, the alt is not working correctly. As the voltage regulator is built in this year alt. it very well could be that the voltage regulator is shot. Another way to check if the alt. is charging, is take a screw dirver and touch the center cap in the rear alt. housing, with engine running. If that center cap is magnitized, the alt is charging.
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Charged battery = 12.60 V at the alternator's stud in the back.
Right after starting = 12.55 V at the alternator's stud in the back.
So, it appears that my alt isn't doing anything... Is there a way to replace the built-in voltage regulator? Or would you guys recommend that I try to locate an alt in a junkyard? (In this case, are 6.9 alts compatible with my factory turbo 7.3?)
Thanks!
Right after starting = 12.55 V at the alternator's stud in the back.
So, it appears that my alt isn't doing anything... Is there a way to replace the built-in voltage regulator? Or would you guys recommend that I try to locate an alt in a junkyard? (In this case, are 6.9 alts compatible with my factory turbo 7.3?)
Thanks!
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Lead Driver
Joined: Mar 2006
Posts: 5,096
Likes: 1,498
From: western SD
The voltage reg. is accesible from the rear of the alternator. It is held on with 2 small bolts IIRC. Any alternator that runs with a v belt from a 6.9 or 7.3 will not work with the serpintine set up that you have, as they mount completly different. If you pull the alternator and take it tto a parts house, the should be able to check it out on their machine. A voltage regulator would be way cheaper than a new alternator.
Postmaster
Joined: Aug 2005
Posts: 4,728
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From: Cleveland, TN
For what it's worth, a friend of mine had a similar problem last year and his problem turned out to be worn out brushes..
NAPA part number ECH F424 The best I remember it was around $11.00 +-
NAPA part number ECH F424 The best I remember it was around $11.00 +-
More Turbo
Joined: Nov 2010
Posts: 521
Likes: 6
From: Cincinnati, OH
I was just going to add that your problem sounds like worn brushes. Fairly common on Fords, the brushes wear out before the other parts give up. The brushes get to the point that they do not make good contact and then no charging. If you feel OK to take the alt aprt, check the brushes and you might just fix it for cheap.
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