Hello all, been reading some of the previous threads on this topic but still have not been able to solve the issue with my Ammeter: it doesn't move.

Let me tell you what I have done thus far for trouble shooting:

With car off, turned on headlights, radio and watched for deflection to left (battery discharging): zero ammeter movement

Turned car over and started engine: no ammeter movement in either direction.

I have owned the car 5 years and the ammeter has never worked.

I've checked for voltage on both terminals of the ammeter separately to ground both indicating 12v. An ohm check across the two terminals yielded ~26ohms. It doesn't appear to have an open winding, and is getting voltage.

I have not pulled the ammeter from the cluster yet or done an inspection of its internal components.

There isnt much stock left on this car. The engine was swapped to a ZZ383 stroker and its also had a manual conversion done to a 5 speed tremec. The starter and alternator obviously are not OEM either.

I mention the above because I've read that sometimes the ammeters do not work well with newer more powerful alternators.. so perhaps that could be a factor? Although I'd suspect I would've seen an open winding in the ammeter or it would be pegged forward when car was running.


Sorry for a rather inconsise post.. thanks all.

 

I suspect it's to do with how it wired. Most ammeters don't actually measure the current flowing from alternator to battery directly, to do that they would need large core cables taken into the passenger compartment. Instead they normally measure the small voltage difference across a cable somewhere between the alternator and battery. You would expect to see 12volts (or something around there) on both wires at the ammeter, but there probably isn't enough voltage difference between where the other ends of these wires are connected to move the ammeter.

 

When I purchased my 76 in November, the ammeter didn’t work. Found the fusible link wire at the starter disconnected and link fried. Fixed that, still didn’t work. Removed the gauge and found the winding broken. Soldered it together and now it works. My 2cents.

 

The ammeter you have (as in all early C3's) is really a galvanometer or millivolt meter, which 'reads' the voltage drop over a fixed length of the main power wire in the engine's wiring harness. That small voltage drop is proportional to the current flowing in that power wire; and the gauge is merely calibrated to read AMPS. It works pretty well...and it does NOT have all that current flowing thru the meter...which is a good thing.
I would bet a pretty good steak dinner that one of the very fine 'connection' wires on the inside of the gauge has been broken (not fried). After many years of service, copper wire gets brittle and a good bump on the road might just cause it to fracture.
The fix? Remove the gauge, open it up, and check the condition of the terminal wires. If you find a broken one, just splice a new piece of fine wire to the terminal, and then to the loose wire. You need to strip the thin lacquer insulation off the old broken wire requiring the splice, so that the solder will stick to it.
It doesn't matter what wire you use, but the finer, the better. Just make sure it is solidly attached to the main terminal, so that it won't flex 'in the wind'.
P.S. Most all of the GM gauges of this type are galvanometer mechanisms. They are just calibrated in different manners and 'fed' by different types of sending units.

 

I suspect you may be right. Although wouldn't my continuity check across the meter terminals have come up as open? It read ~26ohms which didn't seem too odd for a coil.

this seems to be the most likely culprit. I will have to dig into this on the next rainy day.. onto the next problem: my blower motor switch works backwards... high is off and off is high

 

I take it you measured the resistance across the gauge with the wires disconnected. If so, then you are right the internal wires can't be broken. On the other hand if you measured the resistance with the wires still connected, then 26ohms is far too high. The resistance over the length of power wire that 7T1vette mentioned would only be a small fraction of an ohm. I have read of people checking ammeters by putting a 1.5volt battery across them, but I'm not sure if that would risk burning out the gauge.

 

OK so it appears I've found the red flag.. I didn't disconnect the wires from the Ammeter. I should've known better but it was getting late 😕. I will disconnect the leads and try again.

 

Ok so with the leads to the ammeter disconnected and measuring across the terminals it appears the coil is open. I didnt have time to tear the entire console out but I think I will buy a new ammeter since this appears to be 50 years old and has failed once already.

I could start a new thread but my next oddity about this car is the fact that when the blower switch is in the "off" position, it is in fact actually off. I thought the cars were wired to be on low even in the off position? (W. Key "on")

Whats weirder is that if you advance to the next highest position (med-low) it goes to "high".

From here it seems to work opposite.. meaning as you increase the blower speed using the switch it actually decreases the speed of the blower.

Note that the max setting did nothing until I removed the capacitor wired to the blower motor. Once removed the relay picks up and it works normally.

I checked the resistor and without knowing what the actual values are supposed to be, I went by the wiring diagram and it does appear that all the resistors are working with low setting having highest resistance and high have the lowest.

I'm inclined the think something was done to stop the blower from always running when key is on? Or my switch is bad?
I rather like that the blower doesnt run all the time w. Key on, but Id like to have the speed of the blower actually match what the switch indicates

 

A well repaired 50 year-old, GM built ammeter is likely much better than a "brand new" aftermarket ammeter. But, that's just my way of looking at it....

 

You may very well be right, ill take a look at it to see how bad it looks

 

You have to remove it, either way you go. Once it's out, you can open the gauge up and have a look. If you try to repair it and you fail, you've lost nothing but a bit of time and some labor. Then you buy the new one.
But, if you succeed, you save money and you still have an original, WORKING ammeter in your car. Why not try????

 

Sometimes I get impatient, and just want to fix it quick. But you are spot on, the correct thing to do here is attempt to repair the ammeter. In some other threads it looks like I just need to rub the varnish layer off and re-solder the burnt connection.

To be honest I was a bit relieved that the ammeter tested bad as I didn't want to start digging into the wiring since this cars been modified and it could deviate from the factory wiring diagrams in some ways.

Another poster mentioned when he had his engine replaced, they told him he couldn't use an ammeter anymore and had to use a voltmeter from now on... any idea why that is?

 

Yes. Because very few folks know how the GM ammeter really works. So, rather than find our how to reuse it, they just kick it to the dirt and stick a voltmeter in place...which is easy to do (even GM went to voltmeters later!).. The downside of going to the voltmeter is that it won't give you as much information as the ammeter...IF you know how to read it.
If there is an engine change, some will ditch the old [main] wiring harness, which is wired for the ammeter "shunt". That would be a GOOD reason to switch to the voltmeter.

 

FYI: I've repaired two of these over the decades.
It's been my experience both times that the hairwire burns right at the initial connection to the meter.
This means it's an easy repair to simply unwind the next winding to allow enough length to resolder.
You can easily test the meter at that point using a AA battery and/or an ohm meter.
(be careful removing the housing rivets and you may be able to reuse them)

 

Ok, makes sense. I will look through the shop notes from previous owner to see if wiring harness was replaced. I'm leaning towards no

 

I had the same problem on my 75, along with the tach, gas gauge & clock not working.
As stated, a very thin coil wire in the ammeter was broken on mine very close to the terminal. Resolder and a very small piece of heat shrink to insulate fixed it and it's been working for a couple yrs now.
A new aftermarket tach board fixed the tach.
Repaired a broken ground back at the sender fixed the gas gauge.
Couldn't find the open wire on the clock so I punted, set it to perpetual 8:00am and carried on. My aftermarket radio and the wrist watch on my arm both have clocks.
Good luck.

 

My gas gauge works and I assumed correctly, until it read 1/8th of a tank, I filled it up, only took 8 gals 😜

 

The float arm on the sending unit can be bent to better calibrate the system. Do a SEARCH on this to understand the process, so you don't damage the sending unit.

 

Interesting. Im getting nervous now because ive been reading how some of the newer alternators require the ammeter to be converted to a voltmeter?.. i just hate to take the console apart and wind up getting nowhere.


On a side note I I solved the blower motor issue I had. It seems I'm not running the factory wiring harness because the colors of the wires on mine do not exactly match that of the wiring diagrams

My resistor, blower motor, and high speed relay all checked out fine. It was down to a wiring issue or the speed switch.. it appears the low and High speed wires were incorrectly landed to the plug on the resistor end. Swapping the two wires now makes the blower motor speed match the speed indicated by the switch. (It was backwards previously)

also isn't the blower supposed to run all the time if the key is on? Mine will not if the thumb wheel is set to "off" but if the thumb wheel is set to any other setting it will engage the blower motor (w. Key on). Even if switch is set to "off". Just wondering if this is correct?

 

DomJD86
Nothing to worry about. Then new alternators do NOT require you to convert to a voltmeter.
What size is the lead from the alternator to the starter post on your year?
On my 68 it is stock 10-gauge--- which is a bit small for a 140-145 amp capability alternator (it did come with 14-gauge fusible links so the links would open before anything fried and I used it like that for years).
Eventually I replaced the lead from the Horn Relay Bus bar with a 6-gauge lead (with the 10-gauge protection fusible links- which is standard 4-gauge differential for protection). I already had a 6-gauge from the alternator output to the horn relay bus bar.

(the following is from memory so if you want really accurate details I will look it up):I lifted the 10-gauge lead (formerly the main power lead to the starter post) at the Horn Relay Bus bar..... the ammeter still works since it has a lead from the Horn Relay Bus bar and the other leg is from partially down the old 10-gauge lead...which remains attached at the starter post. I didn't feel like calculating where to locate the leg attached to the former 10-gauge lead, so I gambled that it would work ok, and it does.......