kalli

Hi Starfury, I checked on the Mustang wirign diagrams.
up to at least 69 all are labelled AMMETER and wired the exact same.
For a voltage guage I would have suspected ignition+ against ground. None of them wired that way.
I think the gauge label gives that away. I hacve never seen a voltmeter in car as gauge that doesn't show 12. anyway, just wanted to mention ;-)
D/C marking clearly indicates for (DIS)charging. This in my opinion is the only reliable way to see if your alternator works. If it's charging you can measure positive ampere (no matter how small), if discharging its negative.

001mustang

I disconected one alternater wire and OEM ammeter indication continued to flicker near center but battery drained. Ford wouldn't pull our legs w/ this gauge would they? Did it work new? Regardless, it's not nice when gauge fails to normal status.

kalli

leave all connected as is and run without alternator belt. switch on lights and heatermotor. aircon if you have.
Only do this for a BRIEF PERIOD as this usually disables your waterpump and fan as well. Only for testing if interested. you should see the indicator going towards 'D'
there might be an easier way, but i'm not much of an alternator man

001mustang

Wouldn't you think it should go to "C" charging side if a partially discharged battery is used. i could drain batt w/ lights. start car. then closely monitor ammeter for charge indication.

mmaki

All ammeter gauges are essentially voltage gauges in that they measure voltage across a shunt.

In this case they are designed to measure a very small voltage which is the voltage drop across about 3 feet of wire between the battery and the alternator junction. If you follow the alternator b+ wire you will see it goes into the harness a couple feet and then back up to the battery. The ammeter shows whether current is flowing from the battery to the car, or to the battery from the alternator.

I couldn't think of a good way to make this work while improving the wiring and switching to a 3G alternator so I decided the only thin to do way replace the ammeter with a volt meter.

Mike

001mustang

I don't follow why you couldn't wire up the ammeter.

Ammeters can be inconvenient since the wire to and from ammeter must be sized to handle full circuit current. 60+amps ammeter leads for example.

Nice thing about volt meter is wire only has to be sized to support puny volt meter current.

I prefer ammeter but know volt meter is a shoe in. I would like to see wiring diagrams prior to ammeter modification on 67 mustang. Would like to know gauge and path of OEM ammeter wires.

Don't have my diagram w/ me now. Probably online though.

The way I see it is ammeter should measure the current flow in a +12v wire. Ammeter should be installed between alt and batt in 12v+ wire.

Alt charging ==> electrons sent from alt thru ammeter (shows Charging) then into batt + post.

Alt broken and lights on==> electrons pass from batt +post thru ammeter (shows Discharging) to lights and alt dead lug.



If ford OEM "ammeter" only meaures voltage differential across a 3' wire instead of processing the full 60amps thru ammeter then it would have to be very sensitive to provide meaningful data. That would explain why OEM "ammeter" is poor.

I'm leaning toward volt meter to avoid running 60+amp wires for 60amp ammeter.

mmaki

What you describe is often the way ammeters are hooked up, it is not the way it is in the mustang. The ammeter wiring in the mustang caries very little power. One lead hooks up to the battery at the solenoid, the other hooks up to the battery about 3 ft away. It measures the voltage drop over the short length of wire. This wire is intentionally small (about 18 or 16 ga I think) so there is a enough voltage drop across it that the ammeter will respond to it. Now, if you put a bigger alternator in the car, you must increase the gauge of this wire, which will cause less voltage drop and less reading from the ammeter.

Mike

001mustang

I'm leaning more and more toward volt meter.

TexasAxMan

When I rewired my car (Ron Francis kit) I didn't hook up the ammeter. I've found ammeters to be completely useless. I'd like to find a voltmeter that looks like the factory ammeter to switch it out.

scootchu

You can easily swap out an ammeter for a voltmeter. I think a voltmeter can tell you more about the condition of a battery from a quick glance than an ammeter.

An ammeter measures current flowing vs voltage and a reading without the engine running of 12.something indicates what "should" be a good battery. A reading of 13.9-14.1v "should" indicate a charging system that is working.

Swap out your ammeter and the rest of gauges may follow. LOL

I replaced all of my gauges in my 66 and with that I got myself a voltmeter. I do know that an ammeter that is constantly showing "charging" is indicative of a battery that is on it's way out.
Ammeters work, but are harder to read and interpret for some