Won't charge??
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Elder User
Joined: Jul 2008
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this may be a shot in the dark, i had a customer come in with a no charge problem on a 1982 f-150 after a alt change. what had happened was on the back of the alt the reman alt had all insulators black and he had put the field wire from the reg to the stator output post instead of the field post on the alt. may be something to double check
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
I think your problem is the regulator because your running voltage is too low. You can take it to most parts stores and they can test it, but I'm not really sure what the machine does and the test isn't always conclusive. Fortunately a new regulator is pretty cheap anyways.
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Elder User
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Well I don't know what to say except I'm stumpted!! THe battery checks out good, I have two known good regulators and a good alternator. I've checked the alternator harness and that is good as well....If I can get it started whatever the problem is will bring down the charge quickly within 10 minutes. Now I do have a backup light issue as well and I wonder if the problem is connected?? Now befor this problem I added a couple of things, 1 was a wiper delay and 2 I added courtsey lights along with a ash tray light. Right after that is when I started to experience the problem. I plugged the courtsey lights right in the proper plug and in order to get the delay wipers to work correctly (washer function) I had to turn around the plug. Any ideas?
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Elder User
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Ok I think I might be on to something, on the back of my gauge cluster (non gauges) for my alt. light there is a brass bar that jumps from one side of the light to the other. When I installed a new gauge I removed this bar so it's no longer jumping accross. Could this be where I'm getting my drian?? What if I find those to wires and connect them together basically making a complete circut??? FMC400 please respond, sounds like you're good at this stuff.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
I'm pretty sure the brass piece you removed is the shunt resistor for the ALT light. This resistor is necessary to complete the circuit in the ALT light wiring so that the regulator can come online, in the event of the ALT light burning out. Without it, the system would not charge if the ALT light ever burnt out. If your ALT light is burnt out and you have the shunt removed, then your regulator will never come online, and your alternator won't charge.
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Elder User
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I'm pretty sure the brass piece you removed is the shunt resistor for the ALT light. This resistor is necessary to complete the circuit in the ALT light wiring so that the regulator can come online, in the event of the ALT light burning out. Without it, the system would not charge if the ALT light ever burnt out. If your ALT light is burnt out and you have the shunt removed, then your regulator will never come online, and your alternator won't charge.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Looks like we may have found the problem. The best solution would be to put the ALT light and shunt back in. I can't get to any of my schematics right now, but I think if you just jump the ALT light with a short circuit, you'll run 12 volts straight to ground in the regulator, which is bad. I'm pretty sure there needs to be resistance there. Just put it back to the factory setup; the ALT light won't hurt your voltmeter.
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Elder User
Joined: Jul 2008
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Looks like we may have found the problem. The best solution would be to put the ALT light and shunt back in. I can't get to any of my schematics right now, but I think if you just jump the ALT light with a short circuit, you'll run 12 volts straight to ground in the regulator, which is bad. I'm pretty sure there needs to be resistance there. Just put it back to the factory setup; the ALT light won't hurt your voltmeter.
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MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
No. Resistors in parallel do not add; they reduce inversely. For example, if the shunt has resistance R1, and the bulb has resistance R2, then the equivalent resistance is R1*R2 / (R1 + R2). Any resistor you install must have a sufficient power rating to handle the IR drop across the resistor. Resistors in series are what add together (which is not what we're dealing with here).
You might be able to get away with just using the shunt; the regulator is designed to operate this way in the event that the bulb burns out. That is to say, the shunt handles the current to the I terminal in this case. Measure the resistance of the shunt you removed; it should be around 15 ohms.
So, what you're saying is, you literally cut a hole in the cluster where the ALT light used to go? This is unfortunate, because the ALT light is just as important as the regulator; it's an integral part of the charging system.
You might be able to get away with just using the shunt; the regulator is designed to operate this way in the event that the bulb burns out. That is to say, the shunt handles the current to the I terminal in this case. Measure the resistance of the shunt you removed; it should be around 15 ohms.
So, what you're saying is, you literally cut a hole in the cluster where the ALT light used to go? This is unfortunate, because the ALT light is just as important as the regulator; it's an integral part of the charging system.
Posting Guru
Joined: Sep 2003
Posts: 2,313
Likes: 12
From: Northeast LA
I'm not trying to hijack the thread, but i'm having nearly the same issue with my wifes 01Montero Sport. Any insight ya'll might have I'd really appreicate it.
Link to my thread below.
https://www.ford-trucks.com/forums/8...need-help.html
Link to my thread below.
https://www.ford-trucks.com/forums/8...need-help.html
Thread Starter
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Elder User
Joined: Jul 2008
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No. Resistors in parallel do not add; they reduce inversely. For example, if the shunt has resistance R1, and the bulb has resistance R2, then the equivalent resistance is R1*R2 / (R1 + R2). Any resistor you install must have a sufficient power rating to handle the IR drop across the resistor. Resistors in series are what add together (which is not what we're dealing with here).
You might be able to get away with just using the shunt; the regulator is designed to operate this way in the event that the bulb burns out. That is to say, the shunt handles the current to the I terminal in this case. Measure the resistance of the shunt you removed; it should be around 15 ohms.
So, what you're saying is, you literally cut a hole in the cluster where the ALT light used to go? This is unfortunate, because the ALT light is just as important as the regulator; it's an integral part of the charging system.
You might be able to get away with just using the shunt; the regulator is designed to operate this way in the event that the bulb burns out. That is to say, the shunt handles the current to the I terminal in this case. Measure the resistance of the shunt you removed; it should be around 15 ohms.
So, what you're saying is, you literally cut a hole in the cluster where the ALT light used to go? This is unfortunate, because the ALT light is just as important as the regulator; it's an integral part of the charging system.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Let's keep the discussion in the thread in case others run into your same problem some day and would like to read it - what specific trouble are you having? To solve your problem, you will need to put things back to the factory setup. I'm looking at a schematic of a standard Ford regulator and not all the resistances are labelled, so I'm not comfortable saying you can just short the ALT light terminals because I'm not sure how much current that will drive into the regulator. Just from looking at the schematic, it looks like it could shift the voltage drop on the field relay around some; but I can't say for sure. It be best to keep things how the factory has it, then there are no worries.
If you can't replicate the original circuit, I'd get a used cluster from a junkyard. This is my recommendation to you. I have a voltmeter as well; it's part of a gauge cluster I installed on the bottom of my dash. I left the original ALT light in-tact.
If you can't replicate the original circuit, I'd get a used cluster from a junkyard. This is my recommendation to you. I have a voltmeter as well; it's part of a gauge cluster I installed on the bottom of my dash. I left the original ALT light in-tact.
Thread Starter
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Elder User
Joined: Jul 2008
Posts: 557
Likes: 0
Let's keep the discussion in the thread in case others run into your same problem some day and would like to read it - what specific trouble are you having? To solve your problem, you will need to put things back to the factory setup. I'm looking at a schematic of a standard Ford regulator and not all the resistances are labelled, so I'm not comfortable saying you can just short the ALT light terminals because I'm not sure how much current that will drive into the regulator. Just from looking at the schematic, it looks like it could shift the voltage drop on the field relay around some; but I can't say for sure. It be best to keep things how the factory has it, then there are no worries.
If you can't replicate the original circuit, I'd get a used cluster from a junkyard. This is my recommendation to you. I have a voltmeter as well; it's part of a gauge cluster I installed on the bottom of my dash. I left the original ALT light in-tact.
If you can't replicate the original circuit, I'd get a used cluster from a junkyard. This is my recommendation to you. I have a voltmeter as well; it's part of a gauge cluster I installed on the bottom of my dash. I left the original ALT light in-tact.