I have a 69 with the orginal ammeter and alt. The other day I noticed it wasnt moving . I checked the voltage at the alt. and it was fine . Anybody got any ideas before I start taking things apart . My guess is that the gauge died ? Any thing I need to worry about when removing that part of the Dash Its been awhile since Ive had that part off. TX.

 

An ammeter reads amps, not volts. Your alternator can be putting out enough volts but it may not be pushing enough amps.

With an ammeter, most, if not the entire electrical system runs through it. If the ammeter goes bad, more than likely the car won't do anything.

I'd have that alternator tested for amperage output.

 

Often misunderstood, the early C3 ammeter does NOT have all the current going through it. The ammeter is really a millivolt meter which uses a length of the harness wiring [which DOES have the car's current flowing through it] as a shunt. The voltage dropped across that shunt wire is what the meter is actually reading. Now, to the concern posted... If your car's alternator and ammeter are working properly, the meter will almost always show very little movement from the center line. That just means your system is working OK and the battery is fully charged. To see that the meter is working right, just turn the ignition to ON...but don't start the car; then turn on the headlights. The ammeter should read something between 5 and 10 amps to the negative side (discharging). If you leave those lights on for a couple of minutes, then start the car, the ammeter should show somewhere between 10-20 amps to the positive side of the scale (charging). But a good electrical system will have the car fully charged in just a few minutes and the reading will again be close to zero. Hope that helps.

 

I have the same problem on my 68, as 7T1vette says, the ammeter actually measures the voltage difference across a section of the harness, the two points are the horn relay and the starter solenoid.

I haven't fixed mine yet, a PO had botched the wiring at the horn relay that I've repaired, and it looks like another botch at the solenoid that I haven't got to yet. I plan to do it this winter. IIRC, there are fusable links at both ends of the ammeter wiring to these points.

Of course it's after midnight and I've been on the road for 4 days so this is worth the paper it's written on.

 

You got it figured out, POPPA_, now all you need is the time to fix it. P.S. Be sure to use the same size and length wire [as in the original harness] for the "shunt". It doesn't have to be exact; those meters aren't accurate...just very useful.

 

Thanks for all the Ideas guys . I know the ammeter worked well because I have aircraft landing lights for bright lights and those really moved the meter when they were on . Are the shunt wires easily visible or will I need to look for them ? Sorry about the late response but I was behind on the holiday shopping . TX.

 

When I play a song with some bass in it, I can hit +40 and it is fun to watch the ammeter dance, but I don't do that while I'm driving...

 

This is exactly correct.

Here is a marked up schematic I did a while back. It should help you understand how the circuit works.

 

Since the car is still charging I should probably start with the 20or fuse link wires first ?

 

So, are you saying that you tried the engine OFF, ignition ON, lights ON test and there was no needle movement? If so, I can offer you some suggestions.

 

Yes , that needle is dead.

 

OK, it's a different issue. Either a wire going to [either side of] the meter is broken [open]...not the shunt wire or the car wouldn't be operating...., OR one of the coil wires inside the meter has fatigued over time. My guess is that the problem is inside the meter. There's no really good way to test out either without removing the gauge cluster and the ammeter...sorry. Once you dislodge the cluster, label the wiring/meter, then remove the wires to the ammeter. The first thing to try is to take a AA or AAA battery and briefly connect the battery across the ammeter terminals {just a touch and release while you watch the meter}. If it doesn't move, the problem is the ammeter; if it does, the problem is in one of the wires running from the back of the ammeter to the harness "shunt" connection points. If the meter is bad, my advice is to open it up but do as little distress to it as possible. When you get it open, you can look inside and see the coil of very fine wire; there are two wire ends that get soldered to the connection terminals. If one of these wires is broken, that is your problem. Use a very small needle tipped iron to re-solder the wire together. You will have to scrape off the varnish on the end of the broken coil wire to get it to take solder...and you might have to use a small piece of scrap wire to form a jumper to get it connected. Be patient and you can do this. Then to the battery test again. If the needle jumps, the meter is working. Reassemble the meter and use a cotton swab with some Krylon semi-black paint on it to touch up any dings/scratches to the faceplate/rivets. Put it back in the car (wires going to the correct lugs) and it should work for another 10 years, anyway.

 

Thanks a lot ,this is probably whats wrong. Its 39 years old it just wore out . Ill work on this after the Holidays . The car is up on the lift till May so ill have plenty of time to work on it . Happy Holidays and thanks again to all that responded . ill get back to let ya know what happened.