Ammeter diagnosis 1968
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From: Omaha Nebraska
Ammeter diagnosis 1968
I need some help diagnosing my ammeter. I had one originally in the car and it would not read plus or minus when the car was on off using battery or otherwise. I pulled it out and the Gage was stiff and wouldn't allow for the needle to move. I pulled the guts out of it and replaced it with the guts of another ammeter. It allowed me to keep my good face for my 68.
I plugged everything back in and it is registering change. But it's confusing. With the car not running but in the on position I can turn on the interior lights and the blower motor and the ammeter will read in the positive 30 range. If I understand it correctly it should be reading in the negative range.
Any thoughts on what might be causing this?
I plugged everything back in and it is registering change. But it's confusing. With the car not running but in the on position I can turn on the interior lights and the blower motor and the ammeter will read in the positive 30 range. If I understand it correctly it should be reading in the negative range.
Any thoughts on what might be causing this?
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From: Omaha Nebraska
Hmmm
I can only get it on one way due to the nipple on the lower terminal. Here's a picture of what I got. Is it possible I have the wire misplaced at a different mounting location somewhere down the line. I've heard they may end up at the horn relay.
Last edited by Duffeball; May 10, 2020 at 10:27 PM.
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From: Southern MD
The internals of the ammeter is nothing more than a coil of wire wrapped I believe 8 turns. If it is indicating backwards then that would point to the two leads being reversed. Your horn relay looks like it hasn't been messed with for a while. I sort of doubt that is the problem. The black connector at the ammeter, is it keyed or is it possible to spin it 180 degrees and plug it in that way? I really like the ammeter as opposed to a voltmeter. It lets you know quickly when things go south, before you are dead on the side of the road.
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From: Omaha Nebraska
It's a start.
The internals of the ammeter is nothing more than a coil of wire wrapped I believe 8 turns. If it is indicating backwards then that would point to the two leads being reversed. Your horn relay looks like it hasn't been messed with for a while. I sort of doubt that is the problem. The black connector at the ammeter, is it keyed or is it possible to spin it 180 degrees and plug it in that way? I really like the ammeter as opposed to a voltmeter. It lets you know quickly when things go south, before you are dead on the side of the road.
Side note thanks for the compliment on the horn relay. This is part of a frame off and the harness has been completely out of the car. Everything operates flawless. Key buzzer door switches the car runs like a top too. Just gotta get this figured.
Thanks for the input.
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From: Southern MD
It is just a sensing side stream. The actual amperage doesn't go through the gage. Just an indication of the current flow in the system. You are just changing the direction of current flow (that little side stream flow) which will allow your ammeter to read correctly.
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You can remove each wire and its terminal from that plastic connector by inserting a small flat-bladed screwdriver (Jeweler's screwdriver) into the entry point and depressing the retention strip on the metal terminal. Then you can just pull out the wire. Do that for both wires, reverse them and reinsert them into their new "homes". Voila' !
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You can reverse them on the horn relay and it may do the same thing as flipping the plug. I also tried to keep my ammeter to keep it original, but I don’t get it judged and when I got stranded because I didn’t know I lost my alternator belt I switched to a proper colored volt meter. It is a lot better trouble shooting tool and actually tells you something useful
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Difficult to do with the external wiring. Both of the ammeter wires feeds into the main wiring harness bundle and are never seen again! 
That's because the ends of those wires connect the the primary 12vdc load wire, but at different points (about 16" apart). That length of heavy wire becomes a "current shunt" for sending a millivolt signal to the ammeter.
I tell you that so that you will not do some crazy stuff like moving wires around on the horn relay THAT SHOULD NOT BE MOVED. You can reverse those ammeter wires at the gauge; or you can reverse them at the outlet of the fuse block on the engine-side of the firewall. Once they disappear into the main wiring harness, you're done!! Use the Corvette wiring schematic to determine what color wires you need to find coming out of the backside of the fuse block and switch them there, if you have the gauge bezel already installed.
That's because the ends of those wires connect the the primary 12vdc load wire, but at different points (about 16" apart). That length of heavy wire becomes a "current shunt" for sending a millivolt signal to the ammeter. I tell you that so that you will not do some crazy stuff like moving wires around on the horn relay THAT SHOULD NOT BE MOVED. You can reverse those ammeter wires at the gauge; or you can reverse them at the outlet of the fuse block on the engine-side of the firewall. Once they disappear into the main wiring harness, you're done!! Use the Corvette wiring schematic to determine what color wires you need to find coming out of the backside of the fuse block and switch them there, if you have the gauge bezel already installed.
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From: Southern MD
Internally, the ammeter wire should be wound to provide the correct indication when connected to the plug the way it is keyed. If it is backwards internally, then the easiest way to fix it is to swap the wires on the plug at the ammeter. I don't believe that the wiring diagrams are specific enough to say the black and white wire goes to a specific terminal on the ammeter. Swapping the leads at the ammeter will not cause a problem, it will just correct the incorrect indication.
Last edited by ddsmith60; May 13, 2020 at 07:01 PM.
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Last edited by carriljc; May 12, 2020 at 09:20 PM.
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Duffeball - I do NOT have any pictures with the leads hooked up to the gauge. If you don't have an answer by tomorrow send me a PM and I'll go open up my 68. I've done it so many times that it's easy now.
But you really should be able to swap the leads with a couple of jumpers just to test it......
But you really should be able to swap the leads with a couple of jumpers just to test it......
Last edited by carriljc; May 12, 2020 at 09:21 PM.
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This is not 'brain surgery'. With engine OFF and ignition ON, turn on headlamps to create a significant 'discharge' on the ammeter. It should read on the negative side of the meter (-) to show the discharge. If it reads on the positive (+), REVERSE THE LEADS to allow it to read correctly. You either have wires reversed, the wrong ammeter for your car, or the leads reversed at the fuse block/bulkhead connector. Those are the only possibilities for a 'backwards' ammeter reading.