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Discussion Starter · #1 · (Edited)
Symptom: dash ammeter (edit*voltmeter) stays to the left of center 10-13 volt range, When I turn on anything that stresses the alternator voltage drops like a volt. IE. air conditioner. The needle will "sometimes" go to center if the Truck is at idle for long periods of time with no accessories on. Voltage at batteries is 14.4 with engine on

Items that have been replaced: voltage regulator within a year bwd brand, alternator motorcraft high output within a year, brand new interstate batteries within a few months. ground wires to engine block both sides have been cleaned and tightened, An additional grounding wire from block to chassis was added 1/0 welding cable. post connector has been changed as well.

What I have checked: Engine on: Voltage at batteries is 14.4, Voltage from alternator positive to battery ground is 14.4 taken from the yellow-white dot wire. The voltage at the dash voltmeter which is the green-red wire labeled I on the voltage regulator is 13.2 so it not a short in the wire after the voltage regulator cause I'm reading the same voltage at the Voltmeter.

What would cause the voltage regulator to drop like this?

Are there any test I can try ?

My ignition switch was bypassed to a push button, prior owner did this, Could the original switch be shorting out? Any way to test this theory?

edit* The picture below was taken from my 1989 ford shop manual for trucks, I have a 1989 f 250 with a 7.3 idi diesel with an e40d transmission.
 

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Keeping in mind that the gauge in the dash is a VOLT meter, not an ammeter, I don't see anything wrong there. Whenever you put a load on the system, high beam headlights, air conditioner, glow plugs things of that nature it is normal to see a voltage drop. If you were to check the AMPERAGE output, it would most likely go up a little. That is your voltage regulator doing its job. 14.4 volts at the batteries under load with the engine running is normal.
 

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This is why most of the gauges are dumbed down to where they just point in the middle all the time. This is showing normal operation, and you're trying to fix it. There is nothing wrong, and no way to fix it.
 

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Discussion Starter · #6 ·
This is why most of the gauges are dumbed down to where they just point in the middle all the time. This is showing normal operation, and you're trying to fix it. There is nothing wrong, and no way to fix it.
so this was how it came from the factory? where the gauge isn't pointing isn't center? When I mean it will sometimes go to center, I mean if i have nothing on for like a half hour in traffic it will eventually get there but MOST OF the time it's reading 13 volts in my dash.
 

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Discussion Starter · #7 · (Edited)
Keeping in mind that the gauge in the dash is a VOLT meter, not an ammeter, I don't see anything wrong there. Whenever you put a load on the system, high beam headlights, air conditioner, glow plugs things of that nature it is normal to see a voltage drop. If you were to check the AMPERAGE output, it would most likely go up a little. That is your voltage regulator doing its job. 14.4 volts at the batteries under load with the engine running is normal.

sorry voltmeter, rather than ammeter. Isn't that the wire from the regulator that feeds the dash volt meter? Why does the diagram say ammeter I got it from the ford shop manual? Am I reading this wrong? The thing is when I check the batteries when i have those things on, it's still at 14v it's not like 12 volts, so why does the dash say that?
 

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Why does the diagram say ammeter I got it from the ford shop manual?
Shop manuals aren't without mistakes, Oldrebuiltdodge is right, they've been voltmeters for decades. There was a statement in a Detroit Diesel Manual years ago that had me wondering if any factory engineer that wasn't bad enough to fire, got sent down to the basement to compose the shop and owner's manuals. :)
 

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If the meter goes/reads from 0 to 18 it's a Volt meter, if the meter has a 0 in the center and goes/reads to 30 on either side of the 0, it's an AMP meter.
 

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Discussion Starter · #10 ·
Shop manuals aren't without mistakes, Oldrebuiltdodge is right, they've been voltmeters for decades. There was a statement in a Detroit Diesel Manual years ago that had me wondering if any factory engineer that wasn't bad enough to fire, got sent down to the basement to compose the shop and owner's manuals. :)
So assuming it's supposed to be a dumb volt gauge and just point down, why the heck does it bounce around while the batteries stay at 14.4? Was it designed that way? For the record I do know in reality if i leave it alone it doesn't hurt anything since it charges my batteries just fine and truck runs well. But it's like having a girlfriend with a huge zit on her forehead, she treats me well so it's not a deal breaker but I stare at it everyday. I want to oxy that eyesore.

So what would make that voltage regulator 'I' output not 14.4 if charging system is running at 14.4?
 

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Hard to say what's wrong with yours by staring at a computer screen. I'll just say mine and one's in trucks I've driven act like typical voltmeters. The only time the needle will jump back and forth in my pickup is when the glowplugs are cycling back and forth and there's the intermittent voltage drop. Otherwise the needle stays steady right at the 12-14 voltage area.
 

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Hard to say what's wrong with yours by starting at a computer screen. I'll just say mine and one's in trucks I've driven act like typical voltmeters. The only time the needle will jump back and forth in my pickup is when the glowplugs are cycling back and forth and there's the intermittent voltage drop. Otherwise the needle stays steady right at the 12-14 voltage area.

That's what mine does too.
 
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System voltage WILL vary with engine speed, electrical load, and underhood temperature. The gauge is showing those changes. It shouldn't just sit in the middle all the time.

Some of the other gauges WILL sit in the middle all the time because over the years Ford found that people complained when they moved. A good example is the transmissions temperature gauge. It has four positions. Whenever the trans temp is below 50F it's pegged on cold. From 50F to 230F it sits right in the middle of normal. From 230F to 260F it is pointing at the yellow, and above 260F it's in the red. If it were a real gauge they'd have thousands of complaints every winter that the trans won't warm up. So they eliminated all of those complaints.
 

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Depending on the scale, a minor change may not move the needle enough to be detected. I will agree that system voltage will vary.

When I put my 5 gauges on the pillar, I chose wide sweep, large scale so a minor change would move the needle. But then I'm a bit hyper vigilant when I'm rolling down the road @ 19,000 pounds.
 

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1989 ford f250 7.3 idi?
PUT IT IN YOUR PROFILE and signature. As this thread progresses, and as you post in other threads, we'll still need to know this information, and we can't go digging back through all your previous posts to see IF and where you posted it.
...if i have nothing on for like a half hour in traffic it will eventually get there but MOST OF the time it's reading 13 volts in my dash.
There are 2 possibilities: the gauge is accurate, and your system voltage is low & fluctuating so you need to repair the charging system; or the gauge is INcorrect and you need to repair whatever is interfering with it. So step 1 is to measure system voltage with a decent digital multimeter. CLEAN a spot on each battery post (NOT the terminals around the posts), and on the alternator output stud, and on the alternator case. Measure between each pair of clean spots (red to positive; black to negative) with the key off, and again with the engine at high idle and the headlights on. Post all 12 readings so we can tell you what they mean.

...they've been voltmeters for decades.
1987 was the MY that Ford trucks got voltmeters.
...most of the gauges are dumbed down...
On an '89, the only fake gauge is oil pressure.



All the others are real, and work as you'd expect. The ones without numbers aren't calibrated, but they're still reasonably precise.
Why does the diagram say ammeter I got it from the ford shop manual? Am I reading this wrong?
How can we know? You didn't post the diagram, or a link to it.
...the transmissions temperature gauge. It has four positions.
On what MY? I'd like to check out that circuit.
 

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You might want to do some research before you question some people. Mark knows a lot more than quotes from a manual or two. He worked directly for FoMoCo and has been the "go to" guy here for good valid info for years based on actual real work experience.
 

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If your volt meter in the dash is reading low for some time after you stat the engine, you might try checking your batteries for proper charge level. Disconnect them from the truck, and isolate them from one another, because they will back feed. A good load test will determine the capacity of each battery. If one checks out as weak, it is a good idea to replace both of them, because the other probably isn't far behind. If they check out good, and your charging system works, then why worry about it?
 

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Discussion Starter · #18 ·
You might want to do some research before you question some people. Mark knows a lot more than quotes from a manual or two. He worked directly for FoMoCo and has been the "go to" guy here for good valid info for years based on actual real work experience.
Mark seems like a knowledgeable person and I appreciate him looking at my question. But I'm currently trying to research? Sure I made a pretty big error but I'm learning. Now it make sense that an amp meter would increase as the load increases while a voltage would drop. It seems like a no brainer but I took a label from a book without thinking, sorry for my ignorance?

What I was trying to say after I was corrected, was is that wire an actual ammeter or, a mislabeled voltmeter? Was i tracking the wrong wire? I didn't trace the whole green wire through the wiring harness yet. So I did it by referencing the manual which I trusted as gospel ... but now not so much.

Out of curiosity could you tell me some research steps I should do before posting? I searched on the forum, and listed all the changes I've tried from the forum in my first post. Next I thought reading a manual was the next place to start? What should I do first? I'm being serious it's not like I like making a fool of myself by posting incorrect stuff.
 

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We all learn by making fools of ourselves.
 

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Discussion Starter · #20 ·
System voltage WILL vary with engine speed, electrical load, and underhood temperature. The gauge is showing those changes. It shouldn't just sit in the middle all the time.

Some of the other gauges WILL sit in the middle all the time because over the years Ford found that people complained when they moved. A good example is the transmissions temperature gauge. It has four positions. Whenever the trans temp is below 50F it's pegged on cold. From 50F to 230F it sits right in the middle of normal. From 230F to 260F it is pointing at the yellow, and above 260F it's in the red. If it were a real gauge they'd have thousands of complaints every winter that the trans won't warm up. So they eliminated all of those complaints.
oh..... that makes sense? So this was like this from the factory? Good to know. Thanks.

Second question: So the 'I' wire is the voltage underload? Why doesn't the battery voltage at the battery reflect that on my voltmeter? I know it seems like a dumb question but could you explain or tell me what phrase to ask google to get my answer?
 
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