Ammeter terminal question .....

Question here about the relationship between an ammeter gauge front dial and the terminals on the back side of the gauge. This question relates to gauges with the needle pivot on the bottom part of the needle (most common type for old gauges)and the pointer end of the needle facing up.

Do most gauges have the wiring terminals correspond directly to the + or - side that shows on the gauge dial? So looking at the gauge from the front, the left would be the - or discharge on the gauge face, so would the terminal immediately behind that on the back of the gauge be the negative terminal? And the same on the right side but positive?

Seems I remember some gauges being opposite from the front face + and - to the backside terminals. And when wiring up a tractor, you can never be sure except to test what you have hooked up and see what the needle does when the tractor is running and charging?

They are a mixed bag. I make sure i know what they will do by taking a headlight or heater motor and using jumper cables or alligator jumpers to hook up a circuit at the battery.
Hook the Positive marked gauge terminal to the positive Bat post, and the negative gauge terminal to the Light/Motor. Then use a jumper from the other light terminal, or the motor ground to the negative terminal. If the gauge shows - or discharge, I then know how to wire it (either pos ground, or Neg ground depending on the unit I am working on. Jim

I've never seen any polarity markings on meter. When looking at the meter, when electrons flow from the left to right, the meter shows charge.

Electrons flow from negative to positive. So on a positive ground tractor you are saying the right side should be connected to the battery-through the starter switch, and the load charge wires attached to the left? This would allow the lights to draw electrons out of the battery into the light switch, then to the bulbs, then to ground.
I think it would work on some and not others. I have one gauge (Stewart Warner) with Positive marked on the left terminal (looking at the face) a generic gauge with no marks, and a generic gauge with opposite markings.
I just test them with a load on the unit before hookup. Part of the issue is that back in the beginning of electricity scientists got crossed up with the polarity of electrons and discovered their error after systems were being built. Oh well. Jim

Went to pole barn. Took ammeter out of tool box. Connected left post of meter, left post when viewing ammeter from above, to negative of battery. The right side of meter got connected to a light bulb. The other side of bulb got connected to the positive of battery. So when electrons travel from left to right, Ammeter shows discharge.

Electronics 101: Electrons leave the negative post, go throught ammeter, travel through load and return to the positive post.

So when viewing ammeter from above, electrons were traveling left to right, meter showed discharge. This is opposite from what I posted below. SORRY

During charging, electrons are being forced in to the negative post of battery and they come out the positive post. The electrons are traveling in to the right side of ammeter and leaving the right side.

The real test is very simple. Wire up meter, turn key on, meter should show disharge. Turn head lights on, discharge. Turn tractor on, if generator or alternator is working properly, will show charge. Use voltmeter to confirm charging system is working, the battery voltage will increase to around 14-14.6. All the above should work reguardless is you have + or - ground.

I'm sure there are others who have a library full of circuit diagrams for different tractors.

This hopefully answers Crazy Horse's question.

The bottom line is THIS: connect the battery to one side/terminal of the ammeter, and the generator/alternator/charging system and ALL electrical loads to the other side/terminal.

If the meter reads backwards, swap the attached leads between the posts of the ammeter.

If NOT, you are "good to go"!