[66Sprint200]

I have a quick question. Is there a way to tell if my ammeter is working without taking the gauges out? I had replaced all the wiring, and I know everything was hooked up properly, but it's always the same story. I don't know if my ammeter gauge is working. The needle when the car is off is perfectly straight up and down between the D and the C, and when the car is running its the same story. I have never seen the needle move other than when I put those white gauge faces on and when I took them off. Thanks guys.

[1966er]

The manual says turn the key to the "on" position & then turn the headlights on. The gage needle should read in th "D"

[Ivy66GT]

Yes, there is a way to test it and its fairly simple. However, what you see is pretty standard. The full scale deflection is around +-230A so you will almost NEVER see the needle move without a microscope. If you get a needle deflection larger than about the width of the needle there is probably something wrong with your car. That wasn't true for the '65 ammeter but that all changed in '66. See my words here. http://www.allfordmustangs.com/forum...6-mustang.html

The ammeter is wired directly to the starter solenoid. All you have to do to test it is to disconnect the red ammeter wire on the battery post of the solenoid and put a meter in series with the wire. HOWEVER, because of the shunt wiring the maximum current that ever should go through the ammeter is 2.8 Amps at which time there will be 0.64 Volts across the ammeter. The resistance of the ammeter is 0.227 Ohms, calculate it with V=IR. That 2.8 Amps will put the needle to the extreme mark and represent 229 A actually going to or from the battery. Since 229A is ridiculously high, you will NEVER see this condition in use unless the battery cable has shorted to the chassis.

The connections can get dirty and the ammeter will stop working all together. The way its wired the driver will never know since it has no affect upon anything else. Since yours is rewired that shoulnd't be the case though.

The numbers I present are based upon original Ford wiring. Since the calibration is so dependent upon wire sizes, etc., a repro wiring harness might, or might not have the correct wire sizes to make the ammeter work at all.

If you want to see the needle deflect in a meaningful way buy an aftermarket ammeter although you will have to hack the original style harness to install it since the original wiring is not made for a REAL ammeter.

I was going to make a posting with all these details but searching for it now I seem to have never done that.

[Zaikur]

Actually, you don't even have to get under the car. Remove one of the wires to the meter, and place your multimeter in series to the meter and see if you are getting something equivalent to what the ammeter says.

[Ivy66GT]

I find it easier to raise the hood than to grovel and dig around under the dash. The solenoid with the ammeter wire is sitting beside the battery at the front, much easier to get to than the ammeter itself. Also, the '66 gauge is measuring voltage across about a 21" section of 12 gauge wire from the alternator to the battery, it is not really an ammeter. That's why it would be really easy to turn the gauge into a voltmeter except the face markings would be quite odd.

Since the ammeter is wired screwy (with an 80:1 shunt) your series meter will read 1/80 th of what the ammeter is supposed to be showing. If the series meter reads 1 Amp then the alternator is more than maxed out putting 80 Amps into the battery. And in that case the meter needle would still only deflect about 35% of the way to the upper mark. That is why you almost never see that needle move.

[DC Pony]

I turned the key on and turned the lights on and the needle moved about an 1/8 toward charge. I also recently replaced the wiring so I'm wondering if the new harness has smaller/shorter conductors and that would make the gauge act differently.

[1966er]

Originally Posted by DC Pony

I turned the key on and turned the lights on and the needle moved about an 1/8 toward charge. I also recently replaced the wiring so I'm wondering if the new harness has smaller/shorter conductors and that would make the gauge act differently.

Doing it like that should show discharge not charge. Reverse the 2 wires on the back of the meter.