I'm new to the forum, but recognize how much knowledge there is here. I have a '71 (coupe) with an ammeter that doesn't show any movement. Before I fork-out $$$ for an ammeter, what other causes for ammeter problems have you folks found? Also, is there a way to check out the meter once removed from the gauge cluster? Thx.

 

I asked the same thing recently. Search the tech thread for battery guage (gauge). A lot of these guys really know their stuff.

 

Ammeters are pretty rugged. Probably a wiring issue ,use a wiring diagram to check..................

 

This is how it works on my '74, yours is probably the same. The ammeter measures current across a known resistance. One wire (16 gauge black w/ white stripe) goes from my ammeter to the junction block on the fender wall. The other wire (16 gauge black) goes from the ammeter to a splice in the main charging wire (10 gauge red) which runs from the junction block to the starter. The known resistance is the length of charging wire from the junction block to the splice. Each of the ammeter wires terminates in a smaller 20 gauge orange fusible link wire. The fusible link is like a slow blow fuse and keeps the harness from catching fire in case of a short. So it could be the gauge or it could be the fusible link. So to test it disconnect the gauge and test to see if you have continuity to the charging wire i.e. the big red wire at the alternator. cut a wire that will reach from your gauge to the alternator. Clip it to the big red wire then use a multimeter set to ohms to see if you have continuity beween your test wire and the ammeter wires. If you don't have continuity on one of the wires then it is most likely the fusible link and the hard part begins. Untape the harness to find the fusible link and test it for continuity. If it's bad you have to replace it with the exact fusible link wire the same length. Now for the kicker. you can't just replace the link you have to find the short that caused it to burn and fix it.

BTW Welcome to the forum

 

Thanks for the info. I'll let you know what I find out from my testing.

 

I had to re wind mine. Make sure you carefully look at the way it is wond and the thickness before u re-do it.

 

Mine does not work either on the 69...I just check alternator current and test battery occasionally...cause if I get my meat hooks in there,I'll probably hose everything up...

 

It's easy to check the amp meter if it is in your hands. Simply take a standard AA battery and wire it across the amp meter it should move about 5 amps on the scale in one direction or the other. Reverse the wires and it should move the same amout in the other direction.

On these cars the amp meter runs in parallel to a second circuit beween the alternator and the battery (at the starter terminal). Only a percentage of the current goes through the gage. On C1 Corvettes ALL of the generator current runs through the amp gage.

Note that STARTER current never flows through the amp gage on ANY Corvette. It reads current flow (or a percentage of that current) into or out of the battery (supplied from the alternator).

 

better check mine also.

 

Ah, the wonders of the human brain and hands.... Well, I did the continuity tests; and all was good! (no fusible links to deal with) Then I went to the "fun" of removing the gauge cluster. [Fortunately, I am awaiting an original AM/FM Stereo radio, so I had to do that anyway.] Once the ammeter was out, I checked it as suggested---BAD GAUGE! Now, here's where the fun begins. My usual course of action--when I find a defective item that will need replacing--is to tear into it and find the problem. If it can't be fixed, I haven't lost anything...just learned about something I didn't know. BUT, in this case, I found a connecting wire that had become a FUSIBLE LINK (blown open). Knowing the rest of the wiring was OK, I suspect someone tried to put significant amps across it to test it when it was out of the cluster (in it's distant past). Got my trusty pencil soldering iron out..along with some similar wire...and patched it back together. Then I potted the fix in a bit of epoxy resin, just to firm it up and to insulate it. I'm going to wait for it to cure before I put it together and test it. (It still might not work---or even blow again).

Oh, how will I put it together? I used my Dremel to grind off the rivet heads in back of the gauge, punched them out, and SAVED THEM. When I epoxied the wiring, I also epoxied the rivet heads back on the faceplate. Once cured, I'll reassemble the gauge head over the rivet protrusions on the back and epoxy the whole gage onto the faceplate. It's a "one shot" deal, but what the heck, when it goes again THEN I'll buy a new one!

Thanks to all who wrote their great test ideas and suggestions. I love this forum. 7T1vette

 

Year's ago I found the the same problem with my amp meter and corrected it the same way you did. On most windings (motors, gauges, etc) it's the initial post connection (beginning or ending) that fails as it takes the repeated current surge when the circuit is made. If the winding break ends up being too short to simply solder back you can usually get away with unwinding one wrap of the winding and reattaching the, now longer, broken wire.

 

If you need to replace the gauge and are concerned about originality, my mechanic was able to fit the old (grn lines) face on a later body and make it look original. Don't throw out the face.

 

So far, everything appears to work OK. I tried the AA battery test and the needle moved freely. I then semi-assembled the gauge and put it back on its wiring connector, hooked up the juice, and turned on the headlights. Yep! All works OK. Can't say what will happen when the power line sees 30 or 40 amp surge...but I don't think it will be a problem. I suspect that, sometime in the past, there was a dead short for a split second, and the ammeter was the "weak link". If the short had lasted very long, the fusible links would have failed...and they didn't. Who knows? Sometimes the repair lasts longer than the original part! Thanks again for everyone's help.
7T1vette

 

The gage will not see a surge UNLESS the parallel wire in the car is cut or disconnected. If that happens you can roast the amp gage or toast some of the wiring.