Hello Nicholas.
It doesn't sound too hard to fix.
Are you using a GTS dash and wiring loom? That may change the following information somewhat.

You actually aren't reading charge, you are reading the entire electrical system load. In the standard setup, when the engine is running, the ammeter is connected in such a way as to only read the output current of the alternator to the battery, and no other electrical loads . It seems yours has been connected incorrectly.
A 12 gauge red cable runs from the alternator B+ terminal through a firewall grommet to the back of the ammeter. This terminal is located towards the centre of the car, and is stamped "GEN". It is referred to as "G" on the factory wiring diagram. If you have the standard loom this cable will have a "G" label on it.
The other side of the ammeter, (identified as the "B" terminal on the wiring diagram), is stamped "BAT", and has a red 12 gauge cable connected to it (marked with label "B") which goes to the engine harness plug on the firewall. This carries supply to the starter motor solenoid and, eventually, the battery + terminal.

In this way the ammeter is measuring only the output current of the alternator, when running, delivered to the battery.

The electrical loads of the car, including headlights, fans, indicators, and wiper motor are powered from one main cable, which comes from the ammeter. This is an additional cable, which is connected to the GEN terminal of the ammeter, along with the cable coming through the firewall from the alternator.
From your description I believe the main supply cable, which should be connected to the "GEN" terminal, is actually connected to the "BAT" terminal. This means that the ammeter will read every electrical load in the car while the engine is running, which is not what it is designed to do.

When the engine is stopped, and the battery IS being discharged, the ammeter should read about the numbers you described above.

By the way, the wiper motor should have a 15A fuse in the fuse box, which should have blown long before the ammeter was damaged. Not "strengthened" in any way was it?

As far as pulling the dash out goes, you shouldn't have to. Provided you are capable of standing on your head for an extended period both of the brass terminals on the rear of the ammeter are clearly visible from underneath the dash, as are the cable labels and the markings on the rear of the ammeter. (Unless, of course, you have a large air conditioning duct in the way!)You should see one wire on the BAT terminal, and two on the GEN terminal if it is wired correctly.

I hope this helps.

Regards,
Geoff

Edited by user Monday, 19 January 2015 11:49:25 PM(UTC)  | Reason: Not specified

Hi Nick.
Yes. You should have two cables on the "gen" side of the ammeter, one from the alternator, and one to, from memory, the ignition switch, where it's spliced with one or two more cables.
The BAT side of the ammeter has only one cable, which goes to the firewall engine harness plug.

When you've mastered standing on your head, I thoroughly recommend doing a Fiat X19 clutch master cylinder. It's mounted under the dash, inside the car with a remote reservoir. I did one once with my legs hanging out of the sunroof and it took forever. After the quiet sobbing is over you can tell your physiotherapist all about it.
Gotta love Italian cars.

Hi Dr Terry,

Thanks for your advice. I know for a fact that the Gen side definitely had 2 wires going to it when the ammeter went back in. I am hoping that when I get back to the vehicle to inspect the wiring that I find that I have the two wires which do not come from the alternator swapped around onto the wrong terminals. If they appear correct I think I might disconnect the ammeter wires and try to connect another ammeter to the circuit to see if I just have a faulty ammeter (although I suspect that ammeters either work, don;t work or are wired back to front). At least that way i won't have to pull the dash out again (rinking breakage due to brittleness of the plastic) unless I have no other choice.

On the subject of cars that were/are difficult to work on, I do have an Australian example - my sister's now defunct 4 cyl LC Torana S. I have quite large hands and I used to find something as simple as charging the plugs on that thing left me bordering on being curled up in the foetal position in a corner!

Thanks again

Nick

Thanks Nick, although I hope I don't need it. Your ammeter won't need changing, as your description is comprehensive enough to confirm that it is working correctly, and to make me certain that the ignition feed cable is connected to the battery side of the ammeter, and not the "gen" terminal where it should be.

Terry, I'm surprised you didn't include pommy cars in your BBQ list. If not at the top, they must be in the top three.
A well known Morris/mini/Austin workshop in the Eastern suburbs of Melbourne used to have an annual Christmas BBQ and blow up party. Such was the seething resentment of pommy cars that a carefully selected victim, usually either a Morris 1100 or 1500 would get plenty of ignition advance, and then a housebrick placed on the accelerator and let rip at max RPM. A sweep was run on how long it would last.
I think the record was over 20 minutes before it threw a rod.
Murderous, but very therapeutic.

Hi Geoff and Dr Terry,

My ammeter is now working correctly!

Geoff's diagnosis that I had the wiring back to front was correct. I had the main feed from the alternator correctly wired to the GEN terminal on the back of the alternator, but I had the other two wires, labeled B and G on the wrong terminals (still don't know how I managed to do that). I spent 15 minutes with my head under the dash and cross checking the connections against the workshop manual wiring diagram. I swapped the B and G wires over and now the ammeter works precisely as it should. The gauge now correctly reads charge and discharge states and when all accessories are on, registers a far more sensible load.

Thanks for all of your advice/tips. Much appreciated.

Nick