SCARA451

The ammeter gauge in my '71 is just a hair past the middle towards the + side, it never moves to + or - it just stays where it is, as though it is not working. Before I get into the wires I tested the power coming to the gauge with a light tester, someone please let me know if the following makes sense. Started car, made sure the wire harness was hooked up to the gauge(black/white and black wires), attached clip on tester to one of the terminals on the amp gauge touched the other terminal with probe on light, light did not light. Did it a couple of times to make sure it wasn't a bad connection, still nothing. Am I correct in thinking that the light should light if the wires to the gauge were intact ? I am under the impression that the gauge may be good, that the problem is in the wiring to or from the gauge ??? Other info: battery is good and the alternator is charging properly, installed new engine, headlight and a/c wiring harnesses from Lectric Limited all hooked up correctly and working correctly. Is there something that I might have missed or does anyone know what else I can do before I take the dash apart, which I really dont want to get into right now. Thanks for any help !! Right after I wrote this I thought of something else... Started car, put one end of tester to terminal on back of gauge (black wire), grounded other end of tester, test light worked, so I'm getting power TO gauge...put one end of tester to other terminal (black/white wire) grounded other end of tester, test light worked, so I'm getting power OUT of gauge. Put on; lights, radio, hazard's and a/c...GAUGE DID NOT MOVE AT ALL. Am I to assume that the gauge is no good ??? Sorry for the long post.

Yello95

You mean the light on your tester did not light when you connected the clip on one terminal and the other probe to the other amp guage terminal ? Could it be a bad bulb on your tester? have you tested anything else with the tester and did you see the light work?

...otherwise it sounds like you are not getting juice to the guage...trace the wires and see if they are hooked up correctly down the line

...Roger...

Your light is not going to light.You went from pos to pos.If you would have touched ground your light would have lit (if its a good light)

SCARA451

First thing I ALWAYS check is to see if the light works

SCARA451

I edited the original post..please read the addition and let me know if I'm on the right track.

...Roger...

In this link are a couple pics of the fusible link that you should check.
http://forums.corvetteforum.com/show....php?t=2086127

bj1k

No I think you read it wrong. What he is saying is he touched one end of the tester on each terminal at a time while grounding the other end of the tester and he was getting current which means that he has current running through the amp gauge and the gauge doesn't move . Mine does the same thing but everything is charging correctly but my gauge doesn't work and needs to be replaced. Most of the time when these gauges get older , they stop working.

7T1vette

The ammeter in a early C3 does not work like you think. It is actually a millivolt meter that measures voltage drop across a measured length of wire in one of the wiring harnesses (through which current for car operation flows). All you need to do to check the action of the ammeter is to turn your ignition key to "on", DON'T start the car, and turn on the headlights. Your ammeter should show about a 5 to 10 amp discharge. Turn the lights off and the ammeter should go to near zero. A normally operating ammeter will show "0" amps when running and after the battery has had enough run time to fully charge. Immediately after starting the car, the ammeter usually shows about 5 amps charging and that reading will drop to zero as the battery is charged. I'm guessing the ammeter works just fine...but you are not sure how to read it.

...Roger...

Yes that is what he said in his edit.
He should be disconnecting one terminal from the ammeter and then check both leads...if the fusible in the pic I posted is blown then only one of the leads going to the ammeter will be hot

SCARA451

Tested both leads (terminals) on gauge with engine running, both are hot. Just tried what 7T1vette said: Turned key to ON, did NOT start engine, put headlights AND hazards on. Gauge did NOT even flinch.

...Roger...

Try testing with one lead disconnected.If one of the wires is not hot then look for the fusible link under the wiper motor.Check the link I posted above and roll down to the pics.

mrvette

These damn 'amp meters' are the largest stupid problem with lack of understanding and MIS interpretation of the meaning....

first off, forget classical electrical theory/application...this is NOT a classical amp meter by ANY stretch, it is a realtive indicator of wether the bat should be charging or discharging, and that is ALL, there is NO current flowing through this useless gauge (of any true meaning).....

the way to check that junk is.....

key off, engine still.....see that the voltage on the output stud is same as battery+ see that the same essential voltage is on the MOST CLOCKWISE of the two inline blades in the regulator plug.....viewed from the REAR of the alt....that is typically the red wire on any replacement plug from parts house....

if it is not, check the other one, least clockwise....ONE of the two has to be always at +12 IF it's the least clockwise connector, you have it wired backwards, and you have a bad alternator/regulator....guaranfeeekingteed....

so lets assume it's kosher, now measure the least clockwise term, it should be -0- volts....fine.....

turn on the key, engine still....first clock term should be nearly ZERO but a slight voltage....IF you have a dash light it should be lit red and say bat/alt/gen on it....

now start the engine, goose it a bit.....see if the most clockwise wire still has same as alt output.....should be also same as battery unless it's really dead and taking a large charge....


IF you have a bad lightbulb as SOME sharks MAY have....I forget the years of changes....if any....there will NEVER be any voltage on the first clock term...

SO the amp meter is inline with the SECOND term, the MOST clockwise of the two.....it's a realtive indication of alt output....and NOT a true amp meter, screw how i'ts marked....

sears as rowbuck....

7T1vette

The C3 ammeter is designed like most ammeters...it uses a current "shunt" to create a voltage drop which the voltmeter mechanism measures and displays as current draw. The system does draw that amount of current--but it doesn't run through the meter..it only runs through the wire that the ammeter uses as a shunt. That's the way it is, whether you believe it or not. Now, since the headlights don't cause your meter to move, but your car is still working [thus drawing current through the wiring], either the meter is bad or a wire running to the ammeter is broken/open/fried/missing. I believe those are your only choices. My bet is that one of the tiny coil wire leads inside your ammeter failed so that the meter no longer operates. That was how mine failed and, after disassembling it and finding the broken wire, I fixed it by inserting a jumper to reconnect the coil. It has worked fine for about 3 years now. Good luck.

justanotherdoe

If you have a multimeter, check for a short circuit across the gauge when it is disconnected from both wires. It is easy to ground something while swapping a starter, alternator, etc. and burn out the winding of the gauge. If the winding is open, the gauge is broken.

It is not too hard to rewire a gauge, and Radio Shack has the correct wire - you just match the color. Count the number of windings when you take a burned wire off, and replace with the same number of loops. It's a lot cheaper than buying a replacement.

bvanpelt

The ammeter, with its shunt, should sit between the battery connection on the starter and the rest of the electrical system (including the alternator). So it should measure net current flow into and out of the battery (except the starter current). The ammeter should move if you leave the engine off and turn the headlights on.

Someone has put a high-current alternator on my '69, which I believe has toasted the ammeter. I'm voting for replacing this mess with a voltmeter. I just haven't figured out where to get one.

I could just re-wire the ammeter to act as a voltmeter. Painting the dial doesn't sound like much fun...

Anyone have any idea where I can find a voltmeter? Do the later C3's use a voltmeter here?

7T1vette

You can buy later year C3 voltmeters. You just need to get the wiring schematic for that year and wire it into your car using that wiring plan. {Actually, almost all such meters are voltmeters (or millivolt meters). They just get wired up differently [such as adding a shunt for making it an ammeter] to perform different functions.}

bvanpelt

Yep! I'm an EE, and this isn't rocket science. What year did they change over to voltmeters? I'd just remove the existing shunt, wire to IGN & GND, and add a resister, but I want the face to look like a voltmeter and not like I'm charging at 40 amps all the time. -- Brooks

DC3

I read a post on here a while back that said a volt meter from a mid '80s Chevy pickup is the way to go.

DC

mrvette

Correct, that was ME, and I have it for sale, not worth much....

but since it's SO unusual and highly collectible, I need about 1000 bux in payment.....

cash......

any junkyard i'ts damn nearly free, so seek and ye shall find....

wattac2

All that follows is my opinion, and just my opinion:

A functioning ammeter is far better than a voltmeter. The order of usage by GM was ammeter, voltmeter, idiot light. The order, IMO, is correct.

I'd suggest you study the usage of an ammeter. Engine "off" all current flowing from the battery is measured and shown by the ammeter as "negative". This is useful to measure current drain/loads for the various items drawing current from the battery when the engine is off and no alternator to supply any current - lights, radio, courtesy lights, dash lights. If there are any unusual loads they'll show up at this point. Engine running, the ammeter should be in the "+" range showing the battery is being charged. It should remain in the "+" range even with all the accessories/lights on, if not the altenator is suspect. The charging current will be proportional to the degree the battery is drawn down. After a heavy usage the battery should take a "larger" charging current which declines as the battery becomes fully charged. If it doesn't charge, even with a heavy charging current I'd look at a possible "bad" battery. No charging current after heavy usage (long cranking time, lights left on a long time) the battery may need replacing /testing. If the charge current never goes "+" I'd suggest testing the alternator.

All this is very difficult with a voltmeter since you're simutanously measuring the alternator and the battery. They'll "mask" each other and you'll never know what's happening.

Just my opinion.

Andy