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Old 03-21-2010, 10:39 PM   #26
72lb4x4
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Re: Battery/amp gauge

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Originally Posted by VetteVet View Post
Here's the definition of an external shunt ammeter which is what we have in our trucks.

An external shunt is basically a very low value resistor that is in series just as the ammeter was in the previous example, and then the ammeter is in parallel to the shunt. Basically MOST of the current goes through the shunt and only a small percentage goes through the ammeter. By knowing the resistance of the shunt and the meter, the meter is able to calculate the total current by measuring only the small current that goes through the meter. This kind of setup allows small wires to be run to the ammeter in the cockpit, and the high current to remain in the engine compartment. The danger in these setups on some old cars is there isn't a fuse on that small ammeter wire, So if the shunt is damaged or a connector breaks, it would try to flow all the current through the remaining path which is the small ammeter wire and that would melt that wire (along with whatever else it is next to).

This is the reason there are 2 small fuses in the wiring circuit on our trucks that have battery gauges. They are actually amp meters since they measure amperage differential and not volt meters because there is no connection to the negative side of the circuit.
Sorry, but you just don't understand what you're talking about. Your last sentence, among others, proves this.

The meter that reads in amps in a shunt ammeter is still a voltmeter measuring the voltage across the shunt resistor.

Look at the battery gauge and you'll see that it will fry before anything else in the circuit.

You might want to try using a web search to learn what an actual ammeter is and how it works.

The OP may want to look into the differences in the two underhood harnesses to see if they are missing the wires needed to make the gauge work.
Look

Last edited by 72lb4x4; 03-21-2010 at 10:50 PM.
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Old 03-22-2010, 01:28 AM   #27
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Re: Battery/amp gauge

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Originally Posted by 72lb4x4 View Post
Sorry, but you just don't understand what you're talking about. Your last sentence, among others, proves this.

The meter that reads in amps in a shunt ammeter is still a voltmeter measuring the voltage across the shunt resistor.

Look at the battery gauge and you'll see that it will fry before anything else in the circuit.

You might want to try using a web search to learn what an actual ammeter is and how it works.

The OP may want to look into the differences in the two underhood harnesses to see if they are missing the wires needed to make the gauge work.
Look
After going back and re-reading my post I discovered that I mistakenly said the shunt ammeter measures amperage differential. I meant to say voltage differential so I concede that mistake. I also maintain that the external shunt ammeter is neither a volt meter or an amp meter in the exact definition of either. It would be nice if you would point out errors instead of just saying that I don't understand what I'm talking about. It would also be helpful if you would actually contribute to the OP's problem instead of criticizing my post.

While I'll admit I'm not an electrical engineer I do know how to do a web search and I do know how an amp meter works. Your comments are merely semantics .
This web site defines both amp meters and external shunt ammeters.
http://home.cogeco.ca/~rpaisley4/Ammeter.html
There is a voltage drop (differential :edit) across the resistor on the shunt ammeter and while you may call it a volt meter I do not see it referred to as a voltmeter in any of the definitive web sites that I have researched.
Perhaps you can show me where any of the wiring to the battery gauge is connected to the negative side of the circuit. My reference to the lack of fuses in the circuit is correct and if the resistor on the shunt doesn't burn into then the small gauge wire will.
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Old 03-22-2010, 08:51 AM   #28
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Re: Battery/amp gauge

i have to agree with stepside that nothing i try will make this guage work.dont think both of our guages would be bad. hookup makes no sense to me.taking a voltage reading on the same wire a few feet apart gives the same reading. my truck also has no fusable link. maybe there is enough resistance in the link to make a difference?
as far as hooking up the brown wire that used to go to #8 to #5 on the new panel, it works. the system needs a light bulb.instead of the old gen light your using the temp light in the new guage. if the bulb burns out your system wont charge, just like it would with the old panel.
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Old 03-22-2010, 10:53 AM   #29
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Re: Battery/amp gauge

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i have to agree with stepside that nothing i try will make this guage work.dont think both of our guages would be bad. hookup makes no sense to me.taking a voltage reading on the same wire a few feet apart gives the same reading. my truck also has no fusable link. maybe there is enough resistance in the link to make a difference?
as far as hooking up the brown wire that used to go to #8 to #5 on the new panel, it works. the system needs a light bulb.instead of the old gen light your using the temp light in the new guage. if the bulb burns out your system wont charge, just like it would with the old panel.
And there you have it. So why can you not run a resister in place of the light from the brown wire to the external voltage regulator as has been indicated?

BTW I re-read the thread and noticed you mentioned the terminal 5 on the gauge dash was for the temp light in your first post and I missed it. I should have included that in my post where I said terminal 5 dead ends. Sorry about that and hope I didn't cause confusion.
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Old 03-22-2010, 01:28 PM   #30
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Re: Battery/amp gauge

72lb4x4, you last post was a bit harsh I see alot of those statements in the general forums but in the specialized sections (suspension, engine & drivetrain, electrical, ect...ect.) there seems to be a level of mutual respect and when there is a difference of opinion it's more productive to further the discussion. This thread is a perfect example.

neba, 72stepside, The system does make sense if you go back to the basic fundamental that electricity will always take the path of least resistance. The best way to explain this is to imagine a large 6" diameter water pipe with 10 gpm (equivalent to volts) of water flowing through it. If you were to tap an 1/8" line into the 6" pipe not much water is going to flow through it because the 6" pipe offers little or no resistance. Now put a valve (shunt) on the 6" pipe and close it half way you now have a pressure drop on other side of valve which is the electrical equivalent to a voltage drop and the pressure drop (voltage drop) at the end of the 1/8" hose allows water to flow through the 1/8" line the amount of water flowing is equivalent to electrical current which is expressed in amps. Increasing the water supply also increases the pressure drop and more flow thought the 1/8" line or ammeter in our case. So the current flow through the ammeter will be proportional to the current flow through the shunt. The voltage drop at either end has no direct effect on the ammeter other than influencing the direction and amount of current flow which is expressed in amps, so yes it is an ammeter (only measures a small percentage of current flow) and not a volt meter.

Vette, Thanks for verifying the paths on the circuit boards are still there from terminal 5, I don't have spare parts to double check myself also the link you posted on the ammeter is the best I've seen so far and this is a highly debated topic in this and other forums.

72stepside, Have you double checked continuity through the circuit board to the ammeter. Sorry for the long post hope it adds more help than confusion.
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Old 03-22-2010, 08:00 PM   #31
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Re: Battery/amp gauge

i would like to say thanks to all who have tried to help. i wasnt trying to argue, just trying to figure it out. i agree you could add a resister, just seemed easier to plug a wire into empty socket. anyway i dont think those old guages are very accurate and will add an aftermarket set under the dash. thanks again
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Old 04-13-2018, 11:36 AM   #32
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Re: Battery/amp gauge

I'm installing all new wiring harness and 1-wire alternator. My attached diagram the correct way to wire up the battery gauge? Do you have the part number for shunt? Thanks in advance.
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Old 04-13-2018, 04:30 PM   #33
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Re: Battery/amp gauge

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I'm installing all new wiring harness and 1-wire alternator. My attached diagram the correct way to wire up the battery gauge? Do you have the part number for shunt? Thanks in advance.
The wiring diagram you posted may or may not give the desired reading on the meter. It all depends on where you'll be drawing power for the electrical loads in your truck.

For example, if you were planning on using the "BATT" stud on the starter solenoid as your main power distribution point, your meter will only show the output current of the alternator as a "charge". It will never show "discharge" current being drawn from the battery because it's not in the path to measure that current.

Now, if you were to make the right side of the shunt your main power distribution point, the meter will show both "charge" and "discharge" current flowing to or from the battery just like the stock configuration.

The shunt that fixit-p showed back in post #5 is for ChevyII/Nova SS applications and is available from sources such as --> http://www.modernperformanceclassics...s%20Shunt.aspx

However, I see you're showing 4 gauge wiring on your diagram so I assume you're planning on using a fairly high output alternator. I don't know the exact rating on those Nova SS shunts, but I doubt that they are designed to handle much over 60 amps (the largest available alternator on a '65 ChevyII/Nova was a 62 amp unit).

As fixit-p also said in post #5, the "shunt" in these trucks is simply the inherent resistance present in the charge wire ... not a separate component. So the stock "shunt" was a section of 12 gauge wire about 4 and a half, maybe 5 feet long that ran from the junction block on the passenger side fender near the battery, across the radiator support to the factory multi-wire splice that served as the main power distribution point. The current carrying capacity of this system can be increased by using a heavier gauge wire. But that has lower resistance per foot so the sensitivity of the battery gauge will be reduced.

In other words, it would be possible to make the stock battery gauge capable of reading 100 amps or more by using a suitably heavy gauge shunt wire. But it wouldn't be very useful because you wouldn't see much needle deflection at lower currents. For example, with the stock configuration, you can see the needle move to the discharge side if you turn the headlights on without the engine running. But with a larger gauge shunt you might not see any needle movement at all.

With that in mind, I would recommend changing to a voltmeter. That will simplify the wiring and work with most any charging system. I believe member T-Bone converts the '76-'87 style voltmeters to fit '67-'72 gauge clusters.
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Old 09-18-2018, 10:59 AM   #34
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Re: Battery/amp gauge

The in dash battery gauge on my 67 pickup works but only on discharge.
Can't figure it out. I know its charging because I checked with a meter 14.7v.
The truck starts every day without a problem.
Any ideas?
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Old 09-18-2018, 12:00 PM   #35
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Re: Battery/amp gauge

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The in dash battery gauge on my 67 pickup works but only on discharge.
Can't figure it out. I know its charging because I checked with a meter 14.7v.
The truck starts every day without a problem.
Any ideas?
Most likely you've lost the connection on one of the wires to the gauge. There are two wires that go to the gauge and they are both positive. I stress this because some guys think that one wire is positive and one is negative or ground.
Each wire has a small four amp fuse inline to protect the ammeter in case of a short or a high voltage surge. The first place to look is at the fuses and the easiest one to find is on the junction bolt on the right fender. The other one is usually near and below the left headlight in the harness. This is probably discussed in the thread above. Both wires run directly to the dash cluster to terminals 1 and 12 and there are copper strips to the gauge from there. It is common for these connections at the cluster to corrode and lose connectivity. so it may be a case of just cleaning the connections.
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Old 09-22-2018, 04:39 PM   #36
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Re: Battery/amp gauge

Does any aftermarket supplier sell a volt meter to fit the 67 - 72 instrument panel in place of the crappy battery gauge?
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Old 09-22-2018, 06:09 PM   #37
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Re: Battery/amp gauge

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Does any aftermarket supplier sell a volt meter to fit the 67 - 72 instrument panel in place of the crappy battery gauge?
I wouldn't consider the factory battery gauge crappy ... when wired correctly, they actually do a good job of letting the driver know if the battery is charging or being discharged. However, as I described earlier in post #33, they will become less sensitive (and not as useful) if the shunt wire is up-sized to handle a larger current load than stock. And as I mentioned there, member T-Bone converts the '76-'87 style voltmeters to fit '67-'72 gauge clusters.


Quote:
Originally Posted by Ronald29609 View Post
The in dash battery gauge on my 67 pickup works but only on discharge.
Can't figure it out. I know its charging because I checked with a meter 14.7v.
The truck starts every day without a problem.
Any ideas?
In addition to what VetteVet wrote, also check to see how your alternator output is wired into the system. For the battery gauge to function correctly, the alternator output has to be routed to the stock location, which is the multi-wire spliced junction in the harness on the driver side of the radiator support. If the alternator output is re-routed directly to the battery, the battery gauge will only show discharge even when the charging system is working okay.
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Old 09-22-2018, 09:09 PM   #38
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Re: Battery/amp gauge

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Originally Posted by ray_mcavoy View Post
I wouldn't consider the factory battery gauge crappy ... when wired correctly, they actually do a good job of letting the driver know if the battery is charging or being discharged. However, as I described earlier in post #33, they will become less sensitive (and not as useful) if the shunt wire is up-sized to handle a larger current load than stock. And as I mentioned there, member T-Bone converts the '76-'87 style voltmeters to fit '67-'72 gauge clusters.
Yes, you are correct. The factory battery gauge worked fine in the original electrical system, but when we (and in this case, I mean me) "improve" things with larger gauge wire connected from the alternator to the battery terminal on the starter, then that factory system no longer works like it should.
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