# AMMETER HOOKUP HELP!!!

Discussion in 'Trucks and Trailers' started by Sunshine, Feb 1, 2001.

1. ### SunshineLawnSite Memberfrom Colorado Springs, COPosts: 22

Well almost ready for fire in the hole. Got a cheap set of gauges to keep tabs on my new engine. I got the oil pressure and water temp. hooked up fine but for the Ammeter gauge the instructions contradict themselves. The guy at the parts store today said hook one side to the positive back of my alternator and the other to my battery. Does this sound right? Any input would be appreciated.
Thanks Mark

2. ### Power madLawnSite Memberfrom Clatskanie ORPosts: 72

Hey there sunshine
An Amp gage reads current flow, sorta like how much water is running through a pipe. It needs to be wired in series.
Both sides of the gage is "hot". Basicly you are reading how much current(amps) is flowing through a circuit.
The one you want to moniter is alternator current flow(output,draw)
So yes what the parts guy said is right.
I don't know what you have for a dash so I will explain it this way.
You will need to run at least a 12 GA wire from the output side of the alternator to one side of the gage, then from the other side to the + side of the battery.
There are other ways to wire this but it involves the same principles.
But you have to watch what you wire into, because if you wire into say the heater, then you are going to measure the current being used by the heater, not what the alternator is producing.
Hope this isn't even more confusing than it has to be.
Sunshine my butt, my father in law lives in colo sprgs says it's snowing. Ahh well I live in Oregon at least we can daydream about the sunshine LOL
See ya
Ron

3. ### Joseph MeidlingLawnSite Memberfrom Denville, NJPosts: 44

Power mad is right on the money. The Amp gauge reads the flow, and the Voltage can be thought of as the "water pressure". The higher the voltage (pressure) the more electrons that flow and the higher the current, assuming the load resistance stays the same. #12 wire should be fine. As a rule of thumb 14 ga is good up to 15 Amps, 12 ga is good up to 20 Amps and 10 ga for up to 30Amps. Hope this helps. And yes the meter should go in series. There are other "shunt" type meters that don't run in series, but that's a different story.

4. ### SunshineLawnSite Memberfrom Colorado Springs, COPosts: 22

Thanks for the help guys, the last thing the parts guy said was don't mess or I'd burn up my parts- made me nervous when my instructions said to post the positive side to the negative and vice versa.
Power mad it hasn't snowed here for a couple of days so your father in law is in sunshine again. Amazing how a few inches of snow can almost shut this city down, its because they don't start plowing til it quits. I spent my highschool years up in Anchorage, AK- it starts snowing, they start plowing and they don't stop til it quits. Anyways thanks again and by the way I've always got Sunshine, thats what I named my dog. Ha Mark

5. ### wyldmanLawnSite Memberfrom Toronto,OntarioPosts: 182

Be careful !! An ammeter must have all the current the vehicle uses (except starter) running through it to read it properly.If you connect it between the alt and batt it may only read alt output and not show discharge.Also the wire gauges specified are way too low.Fine for an older vehicle putting out 30 amps,but not most newer ones.Hence the reason for shunted type ammeters.They are also alot safer as not all that amperage is running through the vehicle.

To have it work correctly,you have to have the ammeter between the alternator and all the acc loads.If all your power wires for the vehicle are coming off of the alt then it will work fine in between the alt and battery.If some of your loads come off the battery,or starter solenoid post (like most vehicles),then this will not work.

The best way to do it,if it's on your 85 Chevy truck,is pull off the starter solenoid nut,and remove all the wires except the battery cable.Pull them up through to the top of the engine (and remove that stupid steel heat shield tube they run through).

Using 6 or 8 gauge wire (MINIMUM),wire the ammeter between the battery + and the alt output terminal.

Then using another piece of 6 or 8 gauge,run a wire from the alternator positve to the little black plastic junction terminal on the firewall (beside the wiper motor),and connect it and all the wires you pulled from the starter solenoid.If you don't have a junstion block,then put one there.If you have any acc's (ie:driving lights,stereo,etc),they must all pull the power from this terminal,not the battery,or the ammeter won't read any draw they create.If you have a lot of stuff,consider increasing the wire size for you jumper and ammeter wiring to a 4 gauge,just to be safe,and make sure the ammeter you have is rated for high amperage.

Now try it out.With the vehicle off,turn on the headlamps,and the ammeter should swing towards discharge.If it doesn't,just reverse the leads on the back of the ammeter.It should now swing the right way.Start the vehicle and rev it up a bit,and it should swing towards the charge side.Turn on every thing electrical,and with the engine at about 1500 RPM,it should be right in the middle,or slighlty on the charge side.if it shows discharge,then you have a charging system problem.Basically,if the vehicle needs more power than the alternator can put out,it will pull it back through the ammeter and show discharge.If the alternator can overcome this,then the current being pushed to the battery will register a charge on the ammeter.

If wired correctly an ammeter is a very useful tool.If wired incorrectly,it may cause more problems than it is worth.

Consider adding some really good protetive covering over all this wirng,and always use solder and heatshrink,as butt connectors (without soldering) CANNOT handle this kind of current flow.I would also recommend a large maxi fuse or fusible link,or one of those fancy stereo fuse holders,using a fuse rated about 20 amps higher than your alternator.This will prevent a huge fire,if the wiring or alternator or ammeter short out.

Sorry for the long post,but I wouldn't want to see someone ruin their truck over something like this.

6. ### Joseph MeidlingLawnSite Memberfrom Denville, NJPosts: 44

wyldman has a good point. If you are going to run all of the current, not only alternator current, you will need larger wire. If this conductor will see more than 100 Amps think about #4 wire. With the hot ambient temperature under the hood, the combination of current heat (I^2*R) and ambient may cause the connections to fail or the insulation to break down. As a rule of thumb, the larger the current carrying conductor the better. As the cross sectional area of the conductor goes up, the resistance goes down.

7. ### SunshineLawnSite Memberfrom Colorado Springs, COPosts: 22

Huge fire??? Maybe I don't need to hook up the ammeter after all. Thanks for the warning. Mark

8. ### wyldmanLawnSite Memberfrom Toronto,OntarioPosts: 182

Don't get discouraged,it's not that hard.If you don't want to hook up an ammeter,just use a voltmeter instead.One lead to any keyed power souce,and a dsuh ground.Simple

9. ### Power madLawnSite Memberfrom Clatskanie ORPosts: 72

Wyldman
I have a 73 C20 with an ammeter instead of a voltmeter.
This is going through the circuit board. And the last time I checked the alt. output, it was 62 amps. I was looking under the dash and didn't see any welding leads running under there.
How is that wired to handle the current without frying the circuit board?
I'm not trying to be a wise a\$\$, just got me curious is all
See ya

10. ### wyldmanLawnSite Memberfrom Toronto,OntarioPosts: 182

It may be a shunted ammeter,or may not be hooked up correctly.Some ammeters,especially factory,use a shunt,kinda like a resisitor,and measure the current flow across it rather that running everything thru the gauge.A lot safer,but a little less accurate.If yours run thru the circuit board,then it is a shunted factory ammeter.I have also seen some normal ammeters only hooked up with a 12 GA wire,which will work on older vehicle with standard charging systems and very few accesories.An alternator that is rated at 62 amps,will probably only push 40,as they are way overrated.In this case a smaller wire will do.Never hurts to have a larger wire size,but it bites when it's too small and starts causing problems.