AMP Gauge

I think the amp gauge shows how your alternator is working and the volt meter shows your battery charge. If your alternator isn’t charging the battery, the amp gauge shows negative. Just tap the alternator a few times with a hammer as it may just be stuck. If the volt meter is below 12 ( mine has a red light too ), then your batteries may not be at full charge. If that’s the case, don’t shut the truck off unless it’s in or near a shop!

 

Late to the party here, but, amperage is never a set number. voltage is a good indicator of charging state, but amperage is always dynamic. For example, an alternator should always charge between 13.8-14.8 volts, any less and there's a charging issue. However, lights, a/c blower motor, even the fuel injectors will put a differing load based on whatever they need. The truck doesn't even need to be running, and accessories left on can still put a load on the battery, when the alternator isn't even charging. Higher amps drains the battery faster. I've never heard of negative amps. To me (as a mechanic anyway) negative is impossible, or the test leads are backwards. Maybe an amp gauge has a different purpose than what I imagine, as a mechanic I've never seen one.

 

The most useful thing to me about an amp gauge is knowing the battery state of charge, the volt meter doesn't tell you that. If your batteries are low and it cranks slow and long before it starts, the amp gauge will be much higher than normal for a while. Do not shut it off until it comes back down letting you know that the batteries are charged back up. Something my guys are well aware of when they move equipment around the yard for the plow guys. If a truck has been sitting and it's cold, make sure it runs long enough to charge the batteries, or the next time you have to move it, you'll be out there in the snow jumping it.

 

Mine is reaching +150

 

Very low batteries. Check them, charge them or replace them.

After a day or two of long miles if your gauge doesn't come down to 0, or at least start making it's way down to zero, you need new batteries and maybe cables. The one thing this supposedly useless gauge can tell you.

I personally couldn't run without an ammeter.

 

Voltage is loading.

Amp is how hard it's flowing that water in the pipe.

And there is resistance termed Ohms. But let's not go there today. All three are related.

In the truck. Amps. yeesh. It depends on what the alternator is feeding to everything. I have a 190 amper in my tahoe (Previous owner was a rolling music boom box...) but it only volts to between 13.8 to 14.6 if it's a good day.

In a big truck you want the voltage to be stead near 14 all day long. Computers need 9 volts to stay awake and booted. If it falls below 9 it is a brick. No good. It's possible the whole truck will brick on you if it drops below 10 volts these days.

If your alternator quit feeding the whole truck power, your voltage gauge will light a small red light and you will get a computer fault warning code somewhere as well. At that point you are on battery.

Now in the old iron, you have another problem. Belts are potentially gone meaning your oil pump, water pump and anything else attached to same is also gone potentially. (Panty hose fixes this for a while and alot of it.... when you see a strong man buying panty hose that's why...)

Batteries 4 pack will give you 4 hours to get somewhere. But once the voltage drops to 9ish everything computer driven will go away. And there you are sitting on the side of the road. In not so old days we had three in one protection so that three batteries carries the truck while the one is protected from drain for qualcomm etc in emergencies of this nature.

I can go on. But I think that's enough for today about voltage amps and ohms. oooohhmmmm... lolz. /tease/.