rickslt4

I'm installing a Dakota Digital dash in my 73 and it looks like since it does not use an ammeter that I should connect the two wires previously connected to the gauge together?

jnb5101

You could, but it's not necessary. The only current that passes thru the meter is the signal current. The heavy Red wire does all the work.

7T1vette

You DO NOT want to connect those two wires together. Just put a plastic wire-nut or electrical tape on each one.

The two ammeter leads travel to different locations on the same run of large awg wire. If you put them together, high current will be sent through that "loop". Don't do it. Leave them in place for the "next" owner.

jnb5101

The wires to the ammeter run parallel to the #10 red wire between the starter and the horn relay. The ammeter only shows the voltage differences caused by the resistance of that red wire. During discharge the current flows one direction, and while charging the other. It doesn't matter if the wires are connected or not, the total current thru the ammeter is very low-unless the red wire circuit is interrupted.

cardo0

Yes just fold back and tape the ammeter wires.

The C3 corvette ammeter is one of the most confusing instruments on the car. It uses the resistance of some of the wires - including the batt cable - as a shunt. Most owners dont know that if they replace the the batt cable or the alt wire (or a few other wires) with different gauge wire they ruin the calibration of the ammeter. It should still show polarity - whether the batt is charging or discarging - but no longer shows correct amount of charge or discharge in amps. It very difficult to explain to even electrical types because the ammeter looks like its wired in parallel with the batt pos cable and should always read zero. But again it uses the wire/cable internal resistance as a shunt to display current flow direction and amount.

7T1vette

I'm going to say it again, because folks just aren't getting the message. The tiny leads going to the ammeter can not carry that much current. In their usual role (connections to the ammeter) they carry almost NO current. But, if you tie them together, that will form another wire that is in parallel with the main power wire in the wiring harness. That means that 1/2 of the current passing through that harness will be TRYING to pass through that very small awg wire. It will get hot...it will melt...and it will likely catch fire.

LISTEN UP!! And don't do something really, really stupid.

jnb5101

The inherent higher resistance of the smaller wires to the ammeter will cause most of the current to travel thru the larger wire, plus there are two fusible links protecting this circuit.

7T1vette

You, sir, are a fool.

jnb5101

The jury is still out on that, but it may be proven to be true. However, the ammeter itself acts as a true inline meter (as opposed to a volt meter) and has negligible resistance, therefore the ammeter circuit is a "dead short" with or without the meter connected.

7T1vette

THAT ammeter IS a volt meter....a millivolt meter to be exact. It simply reads the voltage drop across a section (about 2 feet) of the main power wire in the electrical harness. That section of wire is used as a current-shunt, and the ammeter reads the voltage drop across it.

Why don't you just do what you are suggesting for someone else to do...and let us know how that works for you? Oh...you might want to make sure your comprehensive insurance is paid up before you fire the engine....

The "jury" will render its verdict based on the results of your "test".

jnb5101

Whatever you say.
But that meter is wired as an ammeter, not a voltmeter. Voltmeters have a resistor in parallel to the meter. without a resistor, all the current must flow thru the meter.

7T1vette

Your "resistor" is the shunt-wire, Mr. Fool. Very low resistance and less than 100 amp current yields a small voltage...just enough to send to a millivolt-meter.

Maxx76

Sorry to interrupt, but I think mr blue corvette is right.


My 2cts...

jnb5101

All analog meters are ammeters, not voltmeters. Their deflection is caused by a magnetic field generated by a current flow. Whether the meter is designed to read amps or volts is determined by how the meter itself is designed and inserted into the circuit. Voltmeters have a voltage divider resistor of high value (that is proportional to the resistance of the meter coil) in series with the meter coil. This resistor limits the current flow thru the meter's fine coil winding. This meter is attached in parallel to a load. An ammeter has an internal shunt resistor of very low value in parallel with the meter coil winding(again, in proportion to the coil's resistance). This shunt resistance must be very low in order not to effect current thru the circuit being measured. It may be a tenth of an ohm or less. For example in this case the coil may have a resistance of 100 ohms and the shunt resistor may be 0.1 ohms. Almost all the current will flow thru the shunt and only a tiny amount will pass thru the meter coil windings to cause a deflection. In the case of our cars, the meter has an external shunt resistor, the #10 Red wire. Most of the charge/discharge current flows thru the Red wire of very low resistance, and a tiny portion thru the meter due to it's higher internal coil resistance. There is no internal voltage divider resistor in this meter. It is wired as an ammeter, and it's circuit resistance is about nil. If it was a voltmeter, how would it indicate a discharge? A negative value? If it was a voltmeter, a single wire could be run from the horn relay to the meter and then the other meter terminal would be to ground.

CaseyJones

No. Play it safe.

7T1vette

jnb...

You are typing words on the computer, but you have no knowledge of vehicle meters. You may be an engineer; but you are completely ignorant of what you are presently discussing.

Desist in trying to convince others you are correct when you really have little or no experience in the details of automotive instruments. Go to the internet and pull up some diagrams and narratives on these items so you can learn about them.

You are not helping anyone by providing BAD information that COULD cause someone to lose their car from a fire resulting from your erroneous info!!
----

I pray that the OP will not listen to this guy, as he knows nothing of what he is discussing.

Maxx76

http://en.wikipedia.org/wiki/Galvanometer
Well, it sounds like the red version now, I'm confused...

jnb5101

As I previously stated, there are two fusible links protecting this circuit. The meter itself has nil resistance, and in essence the circuit is a dead short between the links with the meter connected.

lionelhutz

Geeze, all this arguing over some simple meter wires. Yes, all analog meters are deflected by current flow in the coil. Big freaking deal...


The C3 ammeter itself does not have negligible resistance. I will bet you money that the ammeter in the C3 is not even close to a short. I would expect the meter is at least 100ohms, which is far from being a negligible resistance. Connecting the wires together IS NOT the same thing as having the meter in the circuit between the wires.

The meter is built so it deflects a certain amount when there is a certain voltage applied between it's leads. In other words, the meter spec would be something like 10A displayed per 10mV applied. This is the same as all ammeters that are used with an external shunt. The external shunts are then specified the opposite way, for example have a 10mV drop with 10A of current flow.

As far as the original question - the leads must be isolated. The very best way to do it would be to disconnect the leads under the hood so they are completely isolated. There is absolutely nothing to gain (except a possible fire hazard) by connecting the leads together.

jnb5101

The meter has about 3 feet of 20(approximately) gauge wire in it's coil. Take one apart and see for yourself. I doubt that there is more than 0.5 ohms total resistance in the meter.
But getting back to whether this is a volt or an amp meter do this simple test. Connect a test volt meter to the horn relay and ground. Start the car and watch two meters. The test voltmeter will instantly read 13(approximately) volts when the engine catches and remain steady, while the dash meter will show a high charge rate that tapers off in a few seconds. If the dash meter is acting like a volt meter, how do you explain the difference between the two meters? The dash ammeter is reading current flow, not voltage potential.