Factory ammeters never work, why?

[weim55]

I’ve been around these trucks for decades and never once have I seen the needle move on a factory ammeter, ever.

Thoughts? Fix?

Steve weim55 Colorado

[68 P.O.S.]

Replace the 2 small fuses in the lines. If they're blown, you have to figure out why

[Andy4639]

Originally Posted by weim55

I’ve been around these trucks for decades and never once have I seen the needle move on a factory ammeter, ever.

Thoughts? Fix?

Steve weim55 Colorado

Even when they work they move very little. You will have to watch it all the time to see it moving. It's not like a volt gauge. Very little movement unless you hook something really big amp draw on the battery.

[71gmcC15]

Mine moves all the time. Like when I put the headlights on. The blinkers or start. it. Or jump start some one. It goes to the the right. When running or the left when not. Frim what I can tell it basically just tells a guy when there is load on the altinater and if it's charging with the load on it.

[HO455]

The system isn't the best design as it requires that wiring between the battery, the alternator and the junction block near the horn be in perfect condition and of the factory sizing to allow the amp meter to work. Any changes to wiring size or poor connections changes the resistance balance and the meter will not respond as originally intended.
Count your lucky stars 71gmcC15 your one of the lucky ones.

[projectking]

Originally Posted by HO455

The system isn't the best design as it requires that wiring between the battery, the alternator and the junction block near the horn be in perfect condition and of the factory sizing to allow the amp meter to work. Any changes to wiring size or poor connections changes the resistance balance and the meter will not respond as originally intended.
Count your lucky stars 71gmcC15 your one of the lucky ones.

Count me as another lucky one, I actually have never had one not work. All factory wiring trucks, even my Cummins truck works great!

[Steeveedee]

Guess I'm lucky, too. If the truck has been sitting and has to crank a bit, the needle goes up about half way on the "C" side, which is about 30 Amps- if full scale is 60, and that's about what my alternator is rated at. It comes down fairly quickly, though.

[HIGHWAY BY THE SEA]

When mine did not move for months I checked the two fuses, and they were BOTH blown. I replaced them, and now it moves when I turn the headlights on.

[LockDoc]

-
The ones in my '67, '68, and '72 work but they only move about the width of the needle in either direction. Like Andy said you have to watch really close to see them move.

LockDoc

[57taskforce]

Mine works as well. It the most noticeable when you first start the truck. The headlights will move it a little bit not very much. Normally after about 15 seconds on the first start the needle is back to the center of the gauge.

[weim55]

[QUOTE=68 P.O.S.;8656110]Replace the 2 small fuses in the lines. If they're blown, you have to figure out why[/QUOTE

Where are the fuses you speak of? On the contrary the 64 to 66 Trucks I’ve had the ammeters work perfectly. They will sweep 3/4 of the way to the charge side after starting and settle down to the center. With the engine turned off you can turn on lights and such and it will show a significant discharge.

Steve weim55 Colorado

[57taskforce]

They are on either corner of the core support in little black rubber fuse holders. The fuses are really small glass fuses, I believe they are 2 or 3 amp if I remember correctly.

[slikside]

Originally Posted by 71gmcC15

Mine moves all the time. Like when I put the headlights on. The blinkers or start. it. Or jump start some one. It goes to the the right. When running or the left when not. Frim what I can tell it basically just tells a guy when there is load on the altinater and if it's charging with the load on it.

Ditto! All original wiring...

Originally Posted by HO455

The system isn't the best design as it requires that wiring between the battery, the alternator and the junction block near the horn be in perfect condition and of the factory sizing to allow the amp meter to work. Any changes to wiring size or poor connections changes the resistance balance and the meter will not respond as originally intended.
Count your lucky stars 71gmcC15 your one of the lucky ones.

Time for me to go buy a lottery ticket!

[ray_mcavoy]

Originally Posted by weim55

Where are the fuses you speak of? On the contrary the 64 to 66 Trucks I’ve had the ammeters work perfectly. They will sweep 3/4 of the way to the charge side after starting and settle down to the center. With the engine turned off you can turn on lights and such and it will show a significant discharge.

Yes, as 57taskforce said, one fuse is on the driver side of the radiator support near the voltage regulator. The other is over on the passenger side near the battery. The factory fuse holders take 4 amp SFE4 fuses and look like this:



The 64 - 66 trucks used the same exact ammeter circuit as 67 - 72. So when working properly, the behavior should be the same. However, 64 - 66 did not have the little 4 amp fuses protecting the meter movement and it's associated wiring. I've seen a few 64 - 66 wiring harnesses with melted ammeter wiring so I think adding the inline fuses to those years is a good idea.

[57taskforce]

Originally Posted by ray_mcavoy

Yes, as 57taskforce said, one fuse is on the driver side of the radiator support near the voltage regulator. The other is over on the passenger side near the battery. The factory fuse holders take 4 amp SFE4 fuses and look like this:



The 64 - 66 trucks used the same exact ammeter circuit as 67 - 72. So when working properly, the behavior should be the same. However, 64 - 66 did not have the little 4 amp fuses protecting the meter movement and it's associated wiring. I've seen a few 64 - 66 wiring harnesses with melted ammeter wiring so I think adding the inline fuses to those years is a good idea.

Ahhh... there it is I knew they were less than 5 amp. I replaced my fuses probably close to 5 years ago when I first got my truck running.

[rpmerf]

Mine works with the headlights, but otherwise, hard to notice. I would like to convert to a volt gauge one of these days. There are several threads on converting.

[OregonNed]

Originally Posted by rpmerf

Mine works with the headlights, but otherwise, hard to notice. I would like to convert to a volt gauge one of these days. There are several threads on converting.

The volt (battery) gauge is a great update. I did it recently..

[StingRay]

A little info. The ammeter is a shunted ammeter. It measures the voltage drop across a known resistance. By Ohm's law that voltage drop indicates the amperage flowing across the resistance. That resistance is the wire from the alternator to the battery. As stated any change in the resistance of that connection affects the ammeter. So if you upgrade the alternator and change that wire accordingly the ammeter cannot be used unless you can insert the exact correct resistance and connect those two black wires that are fused across that resistor. The best possible thing is to replace that ammeter with a volt gauge conversion which is much more useful anyway. The only place an ammeter really belongs is in a stock survivor or resto.

[71meangreenc10]

I am happy that the one in old "More-Door" still works but, it does.

Smitty

[maverickmk]

Seems to be more of a novelty than an actual monitoring device. IMO

[HO455]

Originally Posted by StingRay

A little info. The ammeter is a shunted ammeter. It measures the voltage drop across a known resistance. By Ohm's law that voltage drop indicates the amperage flowing across the resistance. That resistance is the wire from the alternator to the battery. As stated any change in the resistance of that connection affects the ammeter. So if you upgrade the alternator and change that wire accordingly the ammeter cannot be used unless you can insert the exact correct resistance and connect those two black wires that are fused across that resistor. The best possible thing is to replace that ammeter with a volt gauge conversion which is much more useful anyway. The only place an ammeter really belongs is in a stock survivor or resto.

Great explanation.

[palallin]

Originally Posted by maverickmk

Seems to be more of a novelty than an actual monitoring device. IMO

It tells you if you are charging or discharging. Anything else really ought to be done under the hood with specialized tools, anyway, so I am satisfied with its utility.

[tdangle]

Mine works, but backwards. Turn the headlights on with the engine off and it swings toward the charge side. Factory stock wiring, never has been altered. I traced it out a while back and its correct. Folks bought the truck new, only thing I can figure is the meter was wired backwards when it was made.

[Stocker]

Mine has worked most of the time I've owned the truck (42+ years). At some point it stopped working due to a blown fuse. A new fuse got it working again.

[WorkinLonghorn]

Mine has always worked just fine and it is interesting information but I always thought that these gauges (temperature, battery charge/discharge, and oil pressure should also have an "idiot light" on the gauge somewhere. I almost lost an engine (and it did fail a few months later) when the fan belt broke causing a very severe overheat. Who drives around monitoring these gauges constantly?