How to wire my ammeter?

[usmile4]

Can I use the stock ammeter guage in my 49 chevy that has been converted to a 12 V system? I know I had to use a resister on the fuel guage, do I need to use one on the ammeter too? There are 2 studs on the back of the guage...what gets wired to each?

[moparsled]

I'm pretty sure amps are amps no matter how many volts, but how many amps is your guage good for and how many amps does your alternator pump? A 100 amp alternator and a 40 amp guage spells F I R E

[usmile4]

It's the stock 49 chevy guage...I don't know what it is rated? The car had been coverted when I got it so I'll have to check on the alternator.

I'm such a novice on these things that I'm dangerous...that's why I'm asking what some people will probably think are dumb questions...but I'm learning!

[Dirty Dug]

The wire from the voltage regulator to the ignition should run through the amp meter.

[HemiRambler]

On my '37 1/2 ton truck I had the factory 6 volt guage hooked up to my 12 volt system - using the output wire directly from the alternator. Was this right?? I dunno but it worked fine. FWIW I have a dump bed on it and it was always fun to watch the amp guage peg in either direction when you hit the dump! I have since changed to a volt guage as I feel it's much safer than running all that current through my harness - but for the record the 6 volt amp guage never failed - had it that way for years. I did eventually blow out the 6volt blower motor:mad:



Can I use the stock ammeter guage in my 49 chevy that has been converted to a 12 V system? I know I had to use a resister on the fuel guage, do I need to use one on the ammeter too? There are 2 studs on the back of the guage...what gets wired to each?

[squirrel]

a 6v ammeter will work fine on a 12v system, although it will probably not move very far, as 12v systems use half as much current as 6v systems.

The ammeter is connected between the battery and the rest of the electrical system. That way it will show you how much current is flowing into our out of the battery. (the big fat wire on the starter goes directly to the batttery, which is the one exception)

They are dangerous things, though, since they have to handle all that current, so use heavy wire, perhaps 10 gage, and be careful with the wiring to keep it away from hot things and sharp edges, and make sure the terminals are tight and well crimped.

[tommy]

Can I use the stock ammeter guage in my 49 chevy that has been converted to a 12 V system? I know I had to use a resister on the fuel guage, do I need to use one on the ammeter too? There are 2 studs on the back of the guage...what gets wired to each?

Yes it will work fine. For it to operate the way the old one did, you need to run the heavy battery wire from the alternator to the amp ga and then down to the battery AND you will need to pick up the power supply for fuse panel somewhere between the amp ga. and the alternator. So if you turn off the ignition and you left the the lights on, the amp ga. will snap over to discharge. If you develop a battery drain in the future, you will see it on the amp ga before you come back to find the battery drained. I always check the ammeter when I get out of the car. It should be in the middle. If it's not I have a problem.

Many of the wiring co.s tell you to hook up the fuse panel feed at the starter solenoid.(they dont do ammeters) If you do, the gauge will never show a discharge if the alternator dies. (that's what the gauge is for!) It's supposed to show which direction the current is flowing... into the battery...(charging) or out of the battery...(discharging).


I put a fusible link (easy to hide) or a circuit breaker in the line down by the battery when I run an alternator with an ammeter. I had an alternator short out (yes they fail too) Because the wire runs through the dash, the cabin filled up with smoke at 30 mph in traffic. It had nothing to do with the ammeter other than the fact that the wire runs inside the cabin. A fusible link will save the wiring and no smoke in the cabin if it it happens again. It's rare but a fusible link is cheap insurance.

[yorgatron]

FUCK ammeters!!! :mad:

run a voltmeter,it's safer and you might notice something wrong before your charging system self-destructs.

[squirrel]

or fuck ammeters AND voltmeters, and run an idiot light. Then you WILL notice there's something wrong.

[4tford]

You are safer using a voltmeter but if you put the fusible link in that will work for using the ampmeter which you already have.

[yorgatron]

there's a hell of an idea :eek:

[desoto]

Voltmeter.......an idiot light with a pointer.


The most informative instrument in your automobile is your ammeter.

[Big Pete]

You'll be ok with the original meter, except it won't be accurate. It will show charge or loss. If the meter seems buried all the time then you'll need to do some math, to properly size the gauge.

The meter belongs in series with the wire off the alternator back to the battery, the one that charges the battery.

Use a meter to prove the battery is charging, and observe forward current. If backward switch meter wires.

[Fifty5C-Gas]

hooked up wrong = FIRE =no more car.

[squirrel]

The most informative instrument in your automobile is your ammeter.

in my car, the most informative instrument is the gas gage

so I know if I'm gonna be walkin or not.

[yorgatron]

the only gauge i care about is the oil pressure.

regular maintenance keeps my charging system working.
i run generators,and they've never stranded me.

[yorgatron]

note to self;fix gas gauge:rolleyes:

[desoto]

hooked up wrong = FIRE =no more car.



Ammeters DON'T cause fires.

If you overload an ammeter it does the same thing a fuse does. It opens up and you have NO connection.

Use a minimum 10 ga. wire

For Negative ground systems(reverse polarity if positive ground):
Passenger's side of most ammeters:
Voltage regulator BAT output
Headlight Switch
Fuse Box
Ignition Switch
etc.


Driver's side of most ammeters.
10 ga. wire to the battery (or to the post on the starter solenoid where the battery cable is mounted)

The neede will only show a substantial charge when you're replenishing the charge depleted from using the starter motor. Once that's put back, the ammeter shuld settle down to just a bit to the right of 0.


FWIW. high output alternators WILL cause fires if they "full filed" which is a pretty common occurance in many aftermarket alternators.

If you're so worried about fires, put a generator on it.

[squirrel]

The thing about ammeters that makes cars with them more fire-prone, is that all the current from the alternator to the battery runs inside the drivers compartment, that's two more trips thru the firewall with that much more risk of lousy wire routing/lack of grommets allowing something bad to happen.

GM gave up on full current ammeters in the early 60s, Mopar was the holdout using them well into the 70s and maybe even later.

I still have the ammeters in my old trucks, never had them burn up, but I do run fusible links on them at the main power connection at the solenoid. And they don't have lots of power robbing accessories to overload the wiring.

Ammeters are fine for those who know how to wire them safely. Voltmeters are probably better for the other folks, but seriously in the late models we have with voltmeters as orig equipment I NEVER look at them! An idiot light will let me knwo if there's a problem with the charging system (which is rare, which is why I never notice the voltmeter).

yorgatron--you'd love my 55, has an idiot light for oil pressure, as well as the charging system, just like Chevy made it. Although the oil idiot light comes on at 20 psi, so it's useful.

[tommy]

The thing about ammeters that makes cars with them more fire-prone, is that all the current from the alternator to the battery runs inside the drivers compartment, that's two more trips thru the firewall with that much more risk of lousy wire routing/lack of grommets allowing something bad to happen.

GM gave up on full current ammeters in the early 60s, Mopar was the holdout using them well into the 70s and maybe even later.

I still have the ammeters in my old trucks, never had them burn up, but I do run fusible links on them at the main power connection at the solenoid. And they don't have lots of power robbing accessories to overload the wiring.

Ammeters are fine for those who know how to wire them safely. Voltmeters are probably better for the other folks, but seriously in the late models we have with voltmeters as orig equipment I NEVER look at them! An idiot light will let me knwo if there's a problem with the charging system (which is rare, which is why I never notice the voltmeter).

yorgatron--you'd love my 55, has an idiot light for oil pressure, as well as the charging system, just like Chevy made it. Although the oil idiot light comes on at 20 psi, so it's useful.

The only thing I'd add is that the same alternator with a volt meter or an idiot light can burn up the wiring and possibly the car too if it fails (without a fusible link). The only difference is the burning wires don't enter the cabin. You don't hear people claiming that alternators are unsafe. Do you? It don't have a damn thing to do with the ammeter.

[desoto]

Excuse me, but if none of the wires enter the vehicle cabin, how does the vehicle run? You guys have been reading too many Ron Francis advertisements. You need to run substantially-sized wires into the cabin to feed the fuse box, headlight switch, ignition switch, power seat relay, power window relay, etc.

The wires that usually end up causing fires are the ones that are run through unprotected holes or across sharp edges under the dash. Wires like the headlight power, the ignition (coil) power, the alternator exciter (it comes off the ignition switch for you laymen). It's usually a small wire that heats up to the point where it melts into an adjacent wire and causes a short circuit. Evenually a main power feed gets involved and you have a fire. Most of the time, though, all you get is a lot of smoke and a bunch of melted wires. Rarely is the main power feed the cause. It's usually something like the coil wire or the electric fuel pump wire that does you in.

Sorry dude, I've been doing this for over 40 years now and I have yet to see an ammeter cause a fire in any vehicle I've ever worked on or in any vehicle I've known about.

An ammeter is like a fsible link. Short out the wire and the ammeter pops just likea fuse.

[desoto]

Oh, and speaking of Ron Francis, here's a guy that is so down on ammeters because they necessitate having to run a large wire into the cabin to carry all that current and what does he use for his whoopdy-do fuse panel? ....an 8 gauge power feed.

Go figure.

[usmile4]

[QUOTE=squirrel] but I do run fusible links on them at the main power connection at the solenoid.

What size fuzible link do I get? Got the part number?

[DrJ]

[QUOTE=squirrel] but I do run fusible links on them at the main power connection at the solenoid.

What size fuzible link do I get? Got the part number?

Buy this book (http://www.themotorbookstore.com/electrical.html) .
It gives step by step instructions on dressing a harness along with how and why each part of the electrical system works.
I wired my truck by it 13 years ago and except for initially blowing one too-small headlight fuse (I mistakenly put a 5 amp fuse in the headlights and it blew when I hit the H4 high beams) I've had zero problems with the wiring.

Oh, yea, DESOTO wrote it!

[rustynewyorker]

My '60 Pontiac damn near burned up one night because the voltage regulator was bad and either adjusted wrong or the contacts just plain stuck in place. This was like 10 years ago now -

I went back out there for some reason after I'd got home and there's smoke coming out of the car - WTF?? Not a lot, but I could smell burning insulation. So I opened the hood to see what was going on. The battery cable connection was glowing faintly red, so I cut the cable right off with some diagonal cutters. Presto, no more smoke.

The wires through the dash ammeter burned the insulation off from the regulator clear through the gauge and back out under the hood. I took the dash top off and I could see the bare, overheated copper - good thing they were wrapped on the outside of the main bundle.

I ended up rewiring the ammeter, which was a pain in the ass, replacing the regulator - if you're going to run one and don't know what shape yours is in, they are not that expensive - and it did something to some other wires, because after that it would not crank off the key switch anymore. I never sorted that out, just added a couple jumpers and push-button under the dash. And I carried an ABC fire extinguisher, a good idea anyways, from then on. I forget what else I had to redo, but I took the time to replace the clock block-off plate with a mini-tach while I had it apart.

So I would highly recommend the fusable links, or a big maxi-fuse which is what the carmakers replaced those with. There are some pictures in the current Street Rod Builder showing how a factory type fusible link can actually flame up when it goes out.


For what it's worth, too, one of the yards I go there is another '60 Pontiac that burned ages ago. It got so hot the dash is slightly warped down in the middle. I'm pretty sure from looking it over that it burned for the same reason, just no one caught it fast enough and the under-dash actually caught fire.

[squirrel]

Excuse me, but if none of the wires enter the vehicle cabin, how does the vehicle run?

There is an extra wire in the cabin, from the alternator to the battery, that is needed with an ammeter, but not with a voltmeter/idiot light.

The rest of what you said makes sense. Cigarette lighter feeds should be on the list too.

[squirrel]

What size fuzible link do I get? Got the part number?

I generally run a #10 power feed wire with a #14 fusible link....does that sound ok guys?

[desoto]

There is an extra wire in the cabin, from the alternator to the battery, that is needed with an ammeter, but not with a voltmeter/idiot light.

The rest of what you said makes sense. Cigarette lighter feeds should be on the list too.


An alternator, if it is shorted to ground whilstbrunning, will toast the diodes and become inoperable. An alternator that goes full field due to a (common) faulty regulator, will toast ANYTHING that is connected to it at the time.

Regardless of where the wires are PHYSICALLY located, the excessive current WINDS UP GOING THROUGH THE CABIN, THROUGH YOUR SWITCHES AND OUT INTO THE DEVICES THAT ARE TURNED ON. Whether you have an ameter, volt meter, idiot light or no charging indicator at al, the current STILL comes inside the cabin.

Now, if the engine ISN'T running, the battery supplies the current and, should a short circuit occur, the current STILL flows inside the cabin until the circuit is broken.

You folks that believe that the omission of an ammeter will eliminate a fire hazard are sorely mistaken. The ONLY fire prevention benefit of runing the charging system output wire directly to the battery is that the least likely wire to catch oin fire is now outside the cabin.

THE HEAVIEST WIRE IS THE LAST TO START TO MELT WHEN A SHORT OCCURS. The smaller wires go first. THAT'S why fusible links are 2 gauges smaller than the wire they're protecting.

Let’s say your engine is running and the feed wire for your headlight switch finally wears through the sharp edge on the dashboard. Since it's probably a 12 or 14 gauge wire, it's going to start melting the insulation as it overloads the alternator and toasts the diodes rendering the alternator inoperative.

The effected circuit runs from the alternator to the sharp edge. Since the alternator output is 10 gauge, it’ll remain relatively cool as opposed to the smaller feed wire going to the sheet metal.

However, without the alternator working, the battery takes over the duty of supplying current to the dead short. Batteries can supply a LOT more current than ammeters can. Look at the CCA numbers on the battery. That’s Cold Cranking Amps. That number’s a whole heck of a lot bigger than the 35 to 120 amps that alternators are rated at. Whether you have an ammeter or not, there’s a lot of potential amperage sitting at the battery end of the power feed wires running into your passenger cabin to make that vehicle of yours function.

Anyway, the alternator to starter solenoid wire (the one you put outside ‘cause you didn’t want to use an ammeter) is nice and comfy and relatively cool as well. Since there’s no output from the alternator, it’s cooled down again and is there for decoration and little else.

Meanwhile, the power feed from the starter solenoid to the headlight switch is now glowing, melting insulation, causing all sorts of alarming smoke to billow out from under the dash and has probably melted a few more wires in the process.

If you had a shunt ammeter inside, the ammeter would have popped like a fuse and the damage would have been minimized.

Wiring doesn’t cause fires in itself but unprotected circuits, especially in vehicles where harnesses are in locations other than where the factory put them, is a recipe for disaster.

[squirrel]

An alternator, if it is shorted to ground whilstbrunning, will toast the diodes and become inoperable. An alternator that goes full field due to a (common) faulty regulator, will toast ANYTHING that is connected to it at the time.

Regardless of where the wires are PHYSICALLY located, the excessive current WINDS UP GOING THROUGH THE CABIN, THROUGH YOUR SWITCHES AND OUT INTO THE DEVICES THAT ARE TURNED ON. Whether you have an ameter, volt meter, idiot light or no charging indicator at al, the current STILL comes inside the cabin.


There's something about E = I R that doesn't make sense about this....if the alternator is running full field, it will not be providing more significantly more current to any resistive load, but it will be providing a lot more current to the battery, through the ammeter.

------------------

The main point you seem to be making is that wire routing is what's important, and I fully agree.....

[Morrisman]

Nothing against ammeters, but I run a voltmeter to tell me how much voltage I actually have in my system, rather than how much is going in, or out, of it at any particular time.

Amps don't mean squat to an electrical meat head like me, but as long as I have more 'n 13 volts on the gauge I guess my system is actually charging, not going flat :)

[desoto]

There is an extra wire in the cabin, from the alternator to the battery, that is needed with an ammeter, but not with a voltmeter/idiot light.

The rest of what you said makes sense. Cigarette lighter feeds should be on the list too.


Actually, thats only half correct.

The portion of the wire that runs from the alternator to the ammeter is eliminated.

The other half, the portion from the ammeter to the battery, is still there as it's what you use to power your vehicle.

[squirrel]

Yes, you're right.

I think one reason that some of us are prejudiced against ammeters, is because we see such creative wiring, like the SW add on ammeter I saw in a 55 Tbird that was wired with lamp cord. Better safe than sorry, so the shotgun approach is to say NO to ammeters.

[4tford]

Yes, you're right.

I think one reason that some of us are prejudiced against ammeters, is because we see such creative wiring, like the SW add on ammeter I saw in a 55 Tbird that was wired with lamp cord. Better safe than sorry, so the shotgun approach is to say NO to ammeters.

I second that! If your new to wiring forget ammeters period. If you know what your doing then the feed is already protected for short circuits and should not be a problem.

[okel]

Voltmeter.......an idiot light with a pointer.


The most informative instrument in your automobile is your ammeter.My amp meter does not show oil pressure

[desoto]

There's something about E = I R that doesn't make sense about this....if the alternator is running full field, it will not be providing more significantly more current to any resistive load, but it will be providing a lot more current to the battery, through the ammeter.

------------------

The main point you seem to be making is that wire routing is what's important, and I fully agree.....


The loads are connected to the system BEFORE the ammeter. A full-fileded alternator will dump it's current through the ignition switch, light switch, fuse box and anything else like power seat and window relays if they're enabled, BEFORE it hits the ammeter.

the battery, being 12 volts above ground potential, will draw less current than a radio, heater, a-c compressor, light bulb, etc. The ammeter will be the last thing to go south when an alternator full-fields.

It's only after the alternator has toasted everything else that the battery (through the ammeter) looks like the best path to ground.

[desoto]

Nothing against ammeters, but I run a voltmeter to tell me how much voltage I actually have in my system, rather than how much is going in, or out, of it at any particular time.

Amps don't mean squat to an electrical meat head like me, but as long as I have more 'n 13 volts on the gauge I guess my system is actually charging, not going flat :)


Depending on where you have your volt meter tied into teh system, you can be as much as 1.5 volts below what's actually "in" your system.

Another consideration is what kind of battery do you have? Lead acid, low maintenance, maintenance-free, Gel, Hybid? Each one requires a different charging voltage. 14 volts on a lead acid battery means heavy gassing and explosion possibility. 14 volts on an Optima battery is barely enough.

Current, on the other hand, is a constant when it comes to monitoring an automotive charging system. One or two amps charge is all you want once teh starte drain is replenished. Anything else points to a problem. It's a simple as that. Regardless of the battery type, if it's more or less than 2 amps charge, you have a problem.

[squirrel]

The loads are connected to the system BEFORE the ammeter. A full-fileded alternator will dump it's current through the ignition switch, light switch, fuse box and anything else like power seat and window relays if they're enabled, BEFORE it hits the ammeter.


What I was getting at, is that alternators do not generate current, they generate voltage. You can't force current into a load! you can only force voltage into a load, and the current the load draws depends on how much resistance it has.

Sorry, my engineering background might be getting in the way of this discussion.

[desoto]

What I was getting at, is that alternators do not generate current, they generate voltage. You can't force current into a load! you can only force voltage into a load, and the current the load draws depends on how much resistance it has.

Sorry, my engineering background might be getting in the way of this discussion.



But a full-fielded alternator is capable of putting out nearly 20 volts, some hotted up ones will even go higher than that. Given that the resistance doesn't change, what happens to the device when too much voltage is applied?

[squirrel]

That depends on the device, doesn't it. Some will short out and draw a lot of current, others will blow out and draw none, others will keep working and draw a bit more current.

[desoto]

That depends on the device, doesn't it. Some will short out and draw a lot of current, others will blow out and draw none, others will keep working and draw a bit more current.

Yup. The wipers will burn out. The headlights will burn out. The stereo will burn out. The cruise control will burn out. The heater will burn out. The MSD may or may not burn out, probably will last for a little while but you never know with those things. Same goes for a stock HEI.

Your engine management computer will go south and your engine will quit. If you're not running a computerized engine the battery, probably the only thing besides the coil that isn't an open circuit, will swell up so big you won't be able to get it out of the battery box if it doesn't explode first.

For the most part, if you don't catch a full fielding alternator right away, especially if you're on the interstate with the alternator spinning at a good clip, your electrical system will be toast.

If you've opted for a high-current affair to power that massive electric fan to keep your Mallory distributor-equipped SBC cool while you tool around the fairgrounds with the a-c and tunes on, you're looking at a pretty quick demise.

If, on the other hand, you have the vacuum advance set up right and your engine runs cool enough that you don't need that fan all the time, you can get away with a 35 amp generator and not have all these issues. :-)

[Big Pete]

On big machines the way is to place a buss link between the battery and everything else, a buss link with known resistance.
Across this buss link a little DC builds and is polarized by current direction.
Buss links "shunts" aren't free, I don't know how to get one free, it probably wouldn't help with the old meter