Ammeter does not show current, but tests out good.

[Brady]

I have a '73 K10 with a 350 in it and manual transmission.  I bought it in 1981 and the ammeter has never worked.  However, I took it out and tested it with a 6v flashlight battery and the needle deflected, indicating current going through it.  The electrical connections are just bolts in the back that plug into a couple of receptacles, so I cleaned them up and tried it in the truck, but no movement at all with the lights on and the engine off.  Same with engine on.

I don't understand what is going on.  There must be another path (shunt) external to the meter, because the battery stays charged up and there is no current going through the meter, elsewise it would be registering some current.

Any suggestions?

TIA,
Brady

[bake74]

     If your meter checks out, then check the wires for the ammeter and where it hooks up to, follow the trail.

[Brady]

That's the problem.  I was hoping someone could give some more detailed info on how to trace it without having to tear apart the whole front of the truck.  I would think that would be a commone problem.

[bake74]

     In the tech section on this forum, type in wiring diagrams, then look up your year and find out where the circuit is, I have used the wiring diagrams many a time to help with ghost problems with my trucks.

[Brady]

Thanks.  Haven't had any more time to work on it.

[muddpuppy01]

the way a ammeter works the power has to travel through it the power has to be on the correct post and the load has to be on its correct post other wise it will read backwards ( positive when discharging and negative when charging )

when you have the meter disconnected does everything still work lights and what not?

Did you have a load on the 6v circuit or just use a 6v battery to short it out

[Bitzer!]

It might be easier to try another gauge before tearing into the loom?

[Brady]

the way a ammeter works the power has to travel through it the power has to be on the correct post and the load has to be on its correct post other wise it will read backwards ( positive when discharging and negative when charging )

when you have the meter disconnected does everything still work lights and what not?

Did you have a load on the 6v circuit or just use a 6v battery to short it out

I didn't try to operate anything with it out, because it seemed to test good.

I just applied 6v across the terminals.  Somewhere I read that a flashlight battery would put out an appropriate current to test it without damaging it.  I was actually searching for what would be the right size resistor in series with it.  I knew better than to use the truck battery directly across it.

[Brady]

It might be easier to try another gauge before tearing into the loom?

I don't have another one of that type to plug in.  I do have one with screw terminals that I could rig up with some probes just to test, when I have time.

[muddpuppy01]

Any load would work a starter would be good to use as it uses a good bit of current.

Just ground out the starter to the neg terminal hook one side of the ammeter to the starter motor terminal. Then take a wire and go from the other side of the ammeter to the pos side of the battery.

If the ammeter shows - then it may be good. Weather it shows the correct amps different story. If it shows + reverse the wires on the ammeter and it should go the other way.

Once you know what side is pos and what side goes to the load. All you would have to do is verify your pos wire and hook it up.