Ampmeter connection

[Raider L]

As soon as I saw it way over to discharge I shut the engine off. So I never gave it time to change, if there was going to be one. Following the instructions about if the needle shows a indication that is wrong, you switch the wires. Okay, doing that, and doing the key to "on" and then headlights, the gauge did nothing but the needle gave the slightest wiggle. Well I was expecting the needle to do some swinging left or right. Do you reckon it's actually indicating correctly and I have such a small load on the system that's all it's going to move? I really don't think that's it. Something else is happening or in this case, not happening.

 

[Raider L]

Okay, I just got through watching a real good video on You Tube by Chris Craft - "How to wire ammeter and volt meter - Amp meter DIY". He showed how the amp gauge indicates so little that he said it would be much more accurate if it was like 15 amps and not 60. He said that when he showed the volt meter reading and the amp meter reading that it was so little indicated on the amp gauge it was hardly noticeable until he hooked up a 40 amp meter and then you could see much more indication.

He said a long time ago when they had "generators" in cars they put amp gauges in cars to show current draw, up or down. But later when they went to "internally regulated alternator's they only needed a volt gauge to show current, or charge back to the battery by the alternator and cars didn't need a amp gauge anymore. He said he doesn't know why people use both a amp. gauge and a volt gauge because all they really need is the volt meter on modern cars. He was using his '70 Chevelle to do the hookups. Now, on his car he has a "horn relay" that he was hooking one of the amp gauge wires to and the other wire from it went back to the 12 volt wire coming off the battery cable to the horn relay. The horn relay was acting as the "shunt", or something between the wires coming from the amp gauge just to show "flow".

Some online sites I've looked at showed the alternator 12 volt wire as one place to hook up one of the amp gauge wires and the other wire to a wire coming from the battery. Well, that's the way I have mine. The wire from the battery is up there on the junction block with the wires going to the starter wiring. Same thing. When I'm looking at his indicated amp draw it was hardly noticeable with the engine running. That's what I saw on mine.

What I need to find is a amp gauge that reads like 0 - 30, then I would see needle movement, the 0 - 60 gauge is is so high it's only going to show the current draw between 12.65 volts engine off to (my alt. puts out 14.2 volts), so 12.65 and 14.20 volts of draw or 1.55 volts, or (I don't know how to do the math to figure out what the amps are in 1.55 volts). I'll try to look it up.

 

[Ellie Niner]

@Raider L Usually, you'll see a slight discharge when you turn the key on and crank the engine (the starter motor itself bypasses the ammeter), then you'll see a fairly hefty swing towards "Charge" after the engine starts... which will start tapering back after a few minutes of running/driving. If your battery is discharged a more than bit, the needle will show a charge for longer before it starts coming back to the middle. An ammeter just shows how much juice is going in to or out of the battery. With the size of your alternator, it may peg or come close to pegging the ammeter for a little bit after a start... You said that it does show a discharge when you turn your lights on with the engine not running, right?

Chrysler switched to alternators across the board in 1961 (or maybe 1960), but used full current ammeters in many of their vehicles through at least the late 1970's.

 

[Raider L]

Well, heck. All I can find is umteen info about car battery amperage hours and all that, and household amperage usage. Somebody who knows the math would need to figure it out for me.

It's my guess that it would be a momentary discharge starting the engine that after it started it wouldn't hardly be showing a charge, at 1.55 volts worth of charge. That's why I said the gauge is working but it's so low it isn't indicating what I expected. I expected the needle swinging over to the +30 to recharge the battery after the started sucked up some juice to start the motor, which it does. Maybe that big discharge was the draw upon starting, and then there would be a small charge period where the needle might move some but not no wild swings! The Chris Craft video showed his Amp. gauge just very slightly past the "0" when the engine started. Maybe that wiggle is it!

After some looking around for 30 and even 20 amp gauges, there are plenty out there on line, I realized that the 60-0-60 gauge that I have is so made that 1 or 2 amps is bearly making the needle move. It's resistive to amps indicating that low either way because it's not that sensitive to that low current. Now, if there was a huge 35 or 40 amp draw on it, that would really show up, big time. But 3 amps won't even show up hardly. The needle will barely move. So, maybe the gauge IS working.

What do 'ya think people?

 

[Raider L]

@Ellie Niner,

Well, there you go. Yeah, it did swing negative a lot right when I started the engine, that's when I got scared I might damage the gauge and right away shut the engine off. So, maybe I needed to have let it go....just a wee bit longer....to see what was going to happen. Of course I had my hands on those big wires under the dash as all that was going on to feel for any heat. It was okay. Right now I can still reach them. After all this is done I'll zip tie them up out of the way.
Another thing is, I'm going to switch wires on the first Autometer gauge that's been in the truck all this time. I never did do that. When it didn't seem to work, maybe that was because it needed the wires switched around, I just unhooked it and took it out. It did cross my mind to first switch the wires, but when it didn't even move I figured I must have damaged it that first time I wired it up wrong. I'll do that tomorrow and see what happens.

 

[Raider L]

I was digging through my stuff and came across this little amp gauge I forgot I had. I may try this one. And lookie there, it's exactly what I said I needed, a 30-0-30 so it won't be so resistant to low amperage. Even though it may still only make it to the first mark, that will be better than such a tiny little indication like the other ones, I couldn't even tell if the darn thing was working or not.

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Make unknown. Does it work? I've had this little gauge for a very long time but it's always been packed up. I'll find out. And it measures 2 1/16" in diam. so I may have to make a surround so it will fit the hole in the panel.

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Now all I need to do with it is find out which post is "A" and which post is "B". Any idea on how to do that? What is the post designation on an Amp. gauge. Is there a standard? When I find out I will mark the letter on this gauge back.

I was taking out my Autometer Amp gauge last night from the instrument panel, and from somewhere, it fell into my hand, a "A" sticker fell off of the back of it. I looked and couldn't tell which post it was attached under. I could see some adhesive residue under each post, but no idea which one had the "A" sticker under it. I have no idea where the "B" sticker is it's gone. I didn't know they were even on the gauge until the other amp gauge I used yesterday had them on the back of the gauge. I had turned it over to look at the back to see how I was going to attach the gauge with a bracket to the back of the instrument panel and there was these stickers.

Actually they were opposite from how I had the wires hooked up on the Autometer gauge from the other day. I assumed the "A" was on the left, like reading from left to right. But the other gauge, that had them on it already were opposite where "A" was on the right post and the "B" was on the left. So, that's why I'm going to try the Autometer gauge but hook the wires up with them switched. Maybe it would have worked if I had the wires on right to begin with.
Boy, I'm telling you, this has been the most confusing thing.

 

[Ellie Niner]

I think you're overthinking this. Don't sweat about hooking up the wires backwards; the only thing that will happen if you do is that the gauge will read backwards. The only real way this circuit will sh¡t on your parade is if one of the wires touches ground, or if you have loose connections.

Just hook up the wires and turn on the headlights with the engine off, and it should show a 10-15 amp discharge. If it shows a 10-15 amp charge, switch the wires around and you're good to go. If the ammeter stays at or near 0 when you do this, then you have wiring that's bypassing the ammeter.

The ammeter will stay fairly inactive under most driving conditions (other than the brief time it takes for the alternator to replenish the battery after you start the engine), as long as the alternator is able to keep up with whatever electrical load you put on it. I do a lot of night driving, and my 66 amp alternator only runs out of breath when I'm sitting at low idle... like waiting at a red light. The longer you have to lean on the battery (alternator unable to keep up with electrical demand), the longer it will show a charge once you get moving again.

 

[Raider L]

@Ellie Niner,

Yeah, I'm prone to doing that when it's something I don't fully understand...like electrics. Reading something tonight it was talking about the amp meter is reading positive on one post and positive on the other post, and all things being equal it would also read correctly if it was one post on negative and the other post on negative, of course it was only using that as an example of the circuitry not how to correctly hook the gauge up.

But what happens if the gauge is defective? The way it's hooked up now with the Alt. going to one post and the other going back to the battery, the only way the battery is being recharged is through the gauge. If the gauge was to fail for some reason then there would be no path back to the battery and the gauge would be showing "0". That's why I thought the Autometer Amp gauge was defective was that it wasn't moving in either direction, hooked up the first way. Tomorrow I'll switch the wires, which I never did and see what it looks like. I just want this to work so I don't have any problems later on.

As the Autometer instructions said, one post would be connected to a positive ( one wire connected to the positive battery post), and the other wire connected to a positive (connected to the battery wire on the starter). That jibs with what I was reading, positive on positive.

What I can't see in my mind is how does the gauge show flow since the only time there would be flow, to the negative, would be as long as the starter is engaged, and once the starter stopped the negative flow would stop and the gauge should slowly go back to the middle. In my mind, watching the gauge it should read discharge until the battery is charged up and at that point it would come to rest at "0". In reality is it going to show discharge when the engine starts and then jump over to charge until the battery is charged and then come to rest at "0", or near enough to it?

And what is the text that I've been reading in various places talking about the resistance of the gauge can't be less than the load or otherwise it will peg the gauge out and damage the gauge. The YouTube I watched by Chris Craft said that the 60-0-60 was to large since these loads are so small. Well, how much current and voltage are we dealing with here? Certainly not full battery power or anything like that is it?

If I'm getting ridiculously repeditive just ignore me, I do that when I fear the unknown.

 

[Ellie Niner]

@Raider L Yep. You are correct that an ammeter will theoretically read the same if wired to the negative side of the system. As it is wired now, everything in your electrical system will pass through the ammeter, except for the starter motor itself (since it draws a few hundred amps and you'd have to run the battery cables through the firewall to measure it, it's easier to just have it bypass the ammeter). This means that the ammeter doesn't pick up the starter's current draw, so the needle won't deflect much when cranking the engine.

I'm not sure how to phrase the way this all works, as it ends up sounding like technobabble gibberish... but it's easiest to think of the ammeter like a water meter. I guess then the starter would be flushing the toilet, and the water to refill the tank (battery) flows through the ammeter. I'm not really following the process on a larger ammeter not reading correctly. At 15 amps, the 60 amp gauge should read approximately 1/4 scale to register 15 amps, while the 30 amp instrument would read 1/2 scale to do the same. I don't think these gauges are going to be 100% accurate under every condition, but they should be reasonably close. The 60 amp one is sized appropriately for your electrical system. I wouldn't worry about burning it out... the current just passes through the ammeter, and that power flow induces a bit of magnetism that tugs the pointer one direction on its way through. There's the tiniest bit of resistance involved, but for all intents and purposes, it's almost nothing. I've never seen an ammeter fail open circuit, though I suppose it's possible. If that were to happen, none of your lights or accessories would work at all. Though there's still power to the starter, the solenoid wouldn't have power so it couldn't crank the engine.

When running, the ammeter is only going to show a discharge when you have more lights and accessories on than the alternator can provide power for (say at idle), making the battery have to kick in and provide the difference. It will only show a charge when the battery needs it and the alternator can provide it... that means if you get a jump start due to running the battery dead, the ammeter will show a charge for a long time... until the battery is fully charged again.

 

[Raider L]

@Ellie Niner,

I understand what you said, and I appreciate your help immensely.
Thinking last night about what you said so far, and from what I've been able to find on line I understood, and some diagrams I've been able to find, and doing some drawings myself of the way the wiring is, and would need to be as far as getting power to go where it looks like it needs to go according to all this, I decided to modify the routing a bit. As far as how I see it in my mind I didn't want the Alt. power to go through this meesly gauge to find it's way back to the battery. It's still basically hooked up like you described and incorporates what I've been able to understand. So, here goes.

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I didn't like the fact that the Alt. wire was going through the Amp. gauge, especially if it doesn't work. The Alternator wouldn't be able to charge the battery due the connection through the gauge, if it fails. So, I put the Alt. wire back to the battery side of the junction "box" (I call it that because that's what it's called on the schematic), I like "the link" as in fusible link. The Autometer instructions say to connect one wire to the battery. Okay, now it's connected to the battery through that other #10 factory wire. And that is the path for the Alt. current to get straight back to the battery. Also from what I read, "positive to positive". The Black #10 I hooked up is left as you can see. That is the first "positive" leg. Okay?

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This is just a pic of another one of those shrinkable ring connectors on the new Alt. wire with the Black Amp. gauge wire and the 12v battery wire there together. Any charging the Alt. does should be detected here, I think, since the Black wire is connected to the alt. wire as well.

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Since these wires have been connected for so long I figured I would give them a good brushing before I hooked anything to this bolt. This is where the other "positive" leg will go.

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The other Amp gauge wire is the yellow ring connector to the right of the bolt just above the "S" wire. You can see it coming in from the right. Since the Autometer instructions say the other wire coming from the Amp. gauge is to go to the starter, then this satisfies that, but still is the power loop more or less in your description.

Originally, all I did was cut all the wires in half that went to the starter, when I rebuilt the truck, took out all the excess that went around the whole engine, and put what was left over on this phenolic block. So the positive battery wire you see here just continued on down to the starter originally.

So where the instructions say connect to the positive battery cable to the starter, well here you go.
We now have the one #10 wire of the amp. gauge, Black, connected to the alt. wire at the link with the other #10 power wire coming from the battery. The first leg of the "positive to positive". The other Amp. gauge #10 wire is going to the starter wire at the bolt making the second "positive to positive" connection, and loop with the amp. gauge in the middle.

Now, does this look okay to you, Ellie Niner?

 

[Raider L]

I attached the wires to the back of the old Autometer gauge and it still doesn't work. I guess it must be damaged from how I had it connected originally, so out it goes. Tomorrow I'll retry that other amp gauge, Auto Gage brand, still Autometer just their econo line, and see if it works. This is getting ridiculous. At some point I've got to get my hands on a amp. gauge that works. The Auto Gage amp gauge did work when I turned the headlights on, but when I cranked the engine that's when it jumped over to neg. 60 and it scared me so I shut the engine off. But I did switch the wires around and nothing happen, it didn't work in either direction. So I don't know what the heck is going on. Maybe I fried that one to, I don't know. I sure as heck don't want to fry my little 30-0-30 vintage gauge doing all this destructive testing. So, no matter what, it's getting put up. I'll just have to wait until next month when I get paid to buy the Autometer "Sport Comp" gauge, like all my others, and try again with a gauge I know I didn't mess up.

 

[Raider L]

@Ellie Niner,

Alright! I went out to the shop to study the schematic so I could look at how the original Amp meter was wired. And this is how the schematic shows it.

From the Amp meter one leg (the Amp meter has two pins on the back that "plug" into the printed circuit that lays over a couple of metal clips to hold onto the pins and the laminated part of the circuit goes to the gang plug). One leg's wire from the gang plug is 18 B 105 that goes down to the fuse block and comes out as 18 B 105A. That wire goes into a fuse holder with a 4 amp fuse and comes out the other side of it as a 16 B 105B. It goes to one of the small posts on the starter solenoid and is one side of the fusible link there. With that wire is #10 R 20 wire. That #10 R 20 wire goes up to the junction block on the firewall. Tory, that is that other #10 red wire with the Alt. wire you were talking about that I was showing you. I'll explain in a minute about that Alt. wire.

The other leg of the Amp meter (we're still talking about the original gauge), connects to wire 18 B/W 106 at the gang plug. It goes through the fuse block and comes out as 18 B/W 106A. From there it goes to a fuse holder with a 4 amp fuse and continues on up to the junction block where it is spliced into the #10 R 20 wire coming from the starter. There's the loop. Both ends of the Amp meter wire were connected together at the junction block with one going to the small post on the starter and the other going directly to the junction block with both ends connected to that #10 red wire. And that's it. the Amp meter is in the middle of both wires.

Now, the Alternator wire. The red power wire comes directly from the Alt. as 12 R 2C and goes straight to the junction block where it is connected to the #10 R 20 wire coming from the starter and that is spliced with the other Amp meter wire. On the same post down there on the starter, is the positive battery wire. All those wires are connected together on the starter and up on the junction block on the firewall.

The way I figured to reroute the Amp gauge wires incorporate your idea of connecting one wire of the Amp gauge to the Alt. wire, which it now is, and the other Amp gauge wire I put on the bolt with the battery wire is exactly like the original schematic shows the original amp meter to be connected, with the Amp gauge in the middle.

Happy?

 

[Raider L]

Now if I could only find a Amp gauge that works we'd both be happy campers!!

p.s. I love reading schematics. It's like when I worked on aircraft. Can imagine how complicated that wiring is?

Wait a minute! Let's go one step further and look on the schematic and see which wire goes to which pin on the original amp meter. That will tell which lug on the back of the Amp gauge to hook which wire. And the answer is... 18 B/W 106A goes to the junction block, that would be the Black wire, and it is the Left pin on the Amp meter . Wire 18 B 105A-16 B 105A on the starter is the #10 Red wire I put on the bolt, and it's the Right pin on the Amp meter. So, looking at the back of the Amp gauge the Black wire goes to the lug on your Right, and the Red wire goes to the lug on your Left. I know that's confusing but when you look at the schematic I'm looking at the pin outs on the gang plug and how they line up with the back of the printed circuit, and how those tracks on the printed circuit go to where the amp meter plugs into the printed circuit.

 

[Ellie Niner]

Now if I could only find a Amp gauge that works we'd both be happy campers!!

p.s. I love reading schematics. It's like when I worked on aircraft. Can imagine how complicated that wiring is?

Well yeah. I'd be happy if your damn ammeter would work as it's supposed to. Everything sounds pretty normal until the thing pegs itself to the discharge side. It doesn't make sense. You shouldn't have anything drawing enough power to do that? Your voltmeter should be dropping at the same time this is happening, if something is really pulling enough to peg the ammeter to discharge.

I'll be honest with you... I've only wired a handful of ammeters, and the only one that was a pain in the ass was an externally shunted one. Maybe two or three were of the full current design, and they just... worked. Did have a factory one in a 1978 Dodge truck that would sometimes get stuck at full charge or discharge on really cold mornings, but that's it. I'm out of ideas at this point.

 

[Raider L]

@Ellie Niner,

Yeah, I came across articles about shunting the wires to the amp meter but mine doesn't need that since the truck had one to begin with. It's just crazy that in the most round about way I came right back to somewhat wiring it just like the factory had it wired. It's not exactly like Autometer showed it to be wired, but it was, and it's not exactly like you suggested wiring it, but it is. You know, it's one of those dang things.

But I wrote all I did about the wiring schematic so that someone else who is trying to understand how to do wiring would get something out of it. This forum's library has the schematic and if anyone would go there and look it up they will be able to see that the way I described the wiring is the way it is. That was my way of understanding it myself.

So, yeah, when I can get a meter that works I don't see any reason why it wouldn't work. I'll tape it all back and put the conduit on the Amp gauge wires and it'll be ready for next month and I'll order a Autometer Sport Comp Amp gauge, and unless I drop the dang thing, like I'm prone to do, it's like the older I get the more clumsy I become. I hate it. I put it in and go through any wire switching necessary and I don't expect any more problems.

In the meantime I appreciate your, and all others input in helping me figure this out. Thanks