Ammeter problem

[Thomas F.]

The ammeter on my 1969 Corvette does not work. I replaced it with a new one and it does not work either. (So I guess both are ok.) I have studied the wiring diagram for this gauge and I get lost trying to trace the wiring. I can't believe how complicated this wiring seems to be. Maybe it is just me. Has anyone had any experience doing this? I can trace the wires to the bulkhead connector, but that is where I get real confused. Thanks for any comments or advice.

[John H.]

Re: Ammeter problem

The ammeter on my 1969 Corvette does not work. I replaced it with a new one and it does not work either. (So I guess both are ok.) I have studied the wiring diagram for this gauge and I get lost trying to trace the wiring. I can't believe how complicated this wiring seems to be. Maybe it is just me. Has anyone had any experience doing this? I can trace the wires to the bulkhead connector, but that is where I get real confused. Thanks for any comments or advice.

Tom-

The black wire from the battery gauge (it's not really an "ammeter") connects to the 10-ga. red main power feed from the big battery cable stud on the starter solenoid via a fusible link splice in the engine compartment side of the engine harness. The black/white wire from the gauge connects to a screw terminal on the horn relay through another molded fusible link splice.

Those two wires sense the voltage at their sources and compare them across the 10-ga. shunt wire from the starter solenoid to the horn relay and display the difference on the gauge face as (+) when current is flowing TO the battery, and as (-) when current is flowing FROM the battery. If you un-plug the connector from the gauge, you should read full battery voltage on each wire, key on or off; if not, one of the wires is loose or broken between the gauge and its source.

[Thomas F.]

Re: Ammeter problem

John thanks for this information. I found a couple of articles in the RESTORER related to these gauges. Both articles traced the problem to a bad or poor connection at the firewall bulkhead connector. I am assuming one or both of these wires pass through the bulkhead connector. This may also be my problem. I will follow your advice and check this out. I would like to get this gauge working before I reinstall my dash. I really appreciate you taking the time to help me with this issue.

[John H.]

Re: Ammeter problem

John thanks for this information. I found a couple of articles in the RESTORER related to these gauges. Both articles traced the problem to a bad or poor connection at the firewall bulkhead connector. I am assuming one or both of these wires pass through the bulkhead connector. This may also be my problem. I will follow your advice and check this out. I would like to get this gauge working before I reinstall my dash. I really appreciate you taking the time to help me with this issue.

Tom -

The black wire goes through the inboard multiple connector, and the black/white wire goes through the outboard multiple connector; terminal corrosion or terminal push-outs are common problems.

[Thomas F.]

Re: Ammeter problem

John, Thanks for bearing with me on this issue. I disconnected the plug from the gauge and tested for voltage at both wires. Connecting the red lead of my test light to the black wire terminal and grounding the black lead my test light lit up but using the same procedure the black/white wire terminal did not light up my test light. If I am understanding what you are saying this indicates I have a broken or bad connection somewhere in the black/white wire. If I run a continuity check on my meter it shows current can flow through the gauge. I assume this is good. It just blows my mind that both wires connecting to the terminals of the meter would indicate 12 volts. Looks like this would cause a short circuit situation.When you refer to the inboard and outboard multiple connectors are you referring to the connectors at the fuse box? This is where I get confused as to where these two wires go.

[Thomas H.]

Re: Ammeter problem

Tom

Even though the wires are both at a 12v potential in reference to battery - (ground), a small voltage (usually in the millivolt range) is developed across the meter terminals depending on the loads being used. This small voltage is what causes the meter to deflect + or - depending on which terminal is at a higher potential. The 12 volts at both terminals can be referred to as a "common mode" voltage (it is common to both terminals). The voltage across the meter terminals is called a "differential mode" voltage. You could think of the meter movement being caused by the small "difference" in voltage between the terminals. The meter is measuring the voltage drop across the wire JZ mentions.

Older cars actually had the meter in line with the 12v feed and if the meter opened up, the charging system would stop working (actually a lot of things would stop working.........)

Tom

[John H.]

Re: Ammeter problem

John, Thanks for bearing with me on this issue. I disconnected the plug from the gauge and tested for voltage at both wires. Connecting the red lead of my test light to the black wire terminal and grounding the black lead my test light lit up but using the same procedure the black/white wire terminal did not light up my test light. If I am understanding what you are saying this indicates I have a broken or bad connection somewhere in the black/white wire. If I run a continuity check on my meter it shows current can flow through the gauge. I assume this is good. It just blows my mind that both wires connecting to the terminals of the meter would indicate 12 volts. Looks like this would cause a short circuit situation.When you refer to the inboard and outboard multiple connectors are you referring to the connectors at the fuse box? This is where I get confused as to where these two wires go.

Tom -

Yes, I'm referring to the harness connectors on the engine side of the fuse block.

Remember that this gauge is NOT an "ammeter" - the last Corvette with an ammeter was 1962. Beginning in 1963, it became a "battery gauge", which carries no circuit loads at all - it's just a sensitive voltmeter (galvanometer) comparing the voltage from two different sources.

[Joe R.]

Re: Ammeter problem

John, Thanks for bearing with me on this issue. I disconnected the plug from the gauge and tested for voltage at both wires. Connecting the red lead of my test light to the black wire terminal and grounding the black lead my test light lit up but using the same procedure the black/white wire terminal did not light up my test light. If I am understanding what you are saying this indicates I have a broken or bad connection somewhere in the black/white wire. If I run a continuity check on my meter it shows current can flow through the gauge. I assume this is good. It just blows my mind that both wires connecting to the terminals of the meter would indicate 12 volts. Looks like this would cause a short circuit situation.When you refer to the inboard and outboard multiple connectors are you referring to the connectors at the fuse box? This is where I get confused as to where these two wires go.

Tom,

An ammeter is designed to measure current and should be nearly a short circuit. It is in series with wire that you are measuring current in. The wires on both sides of the ammeter should be as close to the same voltage as possible.

Edit: What I said applies to actual ammeters like in C1s, not the amps gauge in a C2.
Joe

[Thomas F.]

Re: Ammeter problem

Thanks Joe. Let me see if I am understanding this correctly. My car is a C3 1969. If I test the voltage at each terminal of the connector that connects to my meter I should get a reading of 12 volts on each wire. I am only getting 12 volts on one wire but the engine is not running. Do I need to have the engine running to get a 12 volt reading on the other wire? I appreciate all the help you and the others have given me on this issue. I just want to make sure this meter is working before I reinstall the dash on my car.

[Jim T.]

Re: Ammeter problem

Thomas you will get a reading on both wires with the key off or on and the engine running.

[Richard M.]

Re: Ammeter problem

Thomas,

Since you have 12V at the Black, this comes from the Battery, via the Red wire at the Starter Solenoid stud which has the big Positive cable from the Battery itself. This is the "Source" terminal at the meter. The "Load" terminal on the meter is the Blk/Wht. This is the one that gets a little more complicated, and since you see no voltage there it will require a bit more trickery to find the fault.

If you don't have one.....here is a '69 wiring diagram for reference.http://www.keystonestatecorvetteclub...vette 1969.pdf

But don't get scared if you're not familiar with reading them.......To make it easier for you as I'm unsure if you can follow it along, I created a few marked up wiring diagram pages with some notes, attached below.....It may help you trace the Blk/Wht path. I'm not sure where the bulkhead connector is located exactly, but IIRC the last C3 I worked on, after finding and working up in there, my back hurt for a week.

As you'll see, the Blk/Wht goes through that bulkhead connector. You probably have a bad connection in there, or a broken wire between the gauge and that, or between that and the horn relay buss bar. It's not shown in the diagrams, but there may be a fusible link up by the buss bar connection. A fusible link is like a fuse, but merely a piece of smaller gauge wire which opens up if it's overloaded. You can use your test light to check them......with main car battery disconnected.

As an aside, the Ammeter always has power on one side from the battery(Blk), but will only deflect when there's a load on it, i.e. turn lights on, etc. It'll show negative without the engine running. With the alternator charging you should see a positive deflection on the meter.Just remember to do all of the probing tests and bulkhead contact cleaning with the battery disconnected.Richp.s. Direct download for zoomable views here in the Documents folder on my WS at the bottom of the page.http://home.comcast.net/~richmz/site/?/page/Documents/

......edited with changes to diagram page 2

[Jim T.]

Re: Ammeter problem

The black/white wire goes to a black fusible link near the horn relay. From the fusible link to the actual connection to the horn relay the wire is orange on my original owner 1968. With the battery still connected I would pierce both wires at the entry to the fusible link, very small pierce and verify electrical power at each end of the of the fusible link. I don't know if one could probe into the fusible link to test.

[Richard M.]

Re: Ammeter problem

Jim, Thanks for that info. I updated the diagram to show the Fusible Link. Looking closely, the diagram shows "ORANGE" at that point at the relay buss bar. i missed that before.

Rich

[Thomas F.]

Re: Ammeter problem

Status Report: Thanks to all who helped me with this problem I believe it has been solved. I will only know when I reconnect my ammeter later, but I found that the black wire with the white stripe was not making connection within the bulkhead connector. The female connector for this wire was not locked into position on the fuse box part of the connector and had retracted back into the housing. After I pushed it in until it clicked and reinstalled everything I now have 12 volts of power at the amp connector on both the black/white wire and the solid black wire. This ammeter has not worked since I have owned the car for 15 years, who knows it may have never worked even when it was new.

[Thomas F.]

Re: Ammeter problem

Help! I reinstalled my center cluster and the ammeter or whatever it is called still did respond to any electrical changes. Can anyone tell me if and how this meter can be bench tested before I reinstall my center cluster? I appreciate your help.