Gauge Bench Testing

[Conn47D24]

On now toa  productive topic.

 

One winter project will be to assemble the dash so I can mount it in one piece.

 

Now that engine is running, how can I test my amp gauge ? 

 

Where do the two terminal attached directly w/o the harness?

 

What should it read in the off/ resting posiston ?

 

What am I looking for while the engine runs?

 

 

Thanks all

 

 

Oil gauge is set up temp since my 1st start and is fine.

 

Radimeter tested fine in boilng water on stove

 

I'm not using the gas tank yet so I'll wait on that gauge for now.

 

 

[Loren]

Good job!

Function testing before you install is a great idea.

I test all my batteries before installing (and after removing) them in a device. I find some devices don't tolerate weak batteries but things like flashlights do quite well.

Amp meters are not the most useful of instruments as far as I am concerned. I'd rather have a voltmeter.

To test one set up a battery and a load with the amp meter inline. The needle will dip when the load is applied. If it says CHARGE then swap the leads. The meter is polarity sensitive.

In operation once the battery is charged and there are no loads the meter will read near zero. That's why I don't care for them as most of the time they tell you very little.

An idiot light is more definitive, it's either on or off. But that's found in the next generation of cars.

[greg g]

My ammeter tells me allot.  It moves as the signal light flash, it shadows operation of the dimmer switch, with the way I have my brake lights wired it shows a step up in Genny out put when brakes are applied. With the engine off and the ign switch off I can see haw many amps my lights draw,with key in run I can see how many amps the three posisitions of the heater fan draw.  And it tells me the general charge statof the battery by how quickly it drops down to minimal charge after starting the car.  My volt gauge basically sits there at 6.7 volts when the engine is running.  Maybe I am just better of reading between the lines.

[Loren]

On 11/22/2019 at 7:43 AM, greg g said:

My ammeter tells me allot.  It moves as the signal light flash, it shadows operation of the dimmer switch, with the way I have my brake lights wired it shows a step up in Genny out put when brakes are applied. With the engine off and the ign switch off I can see haw many amps my lights draw,with key in run I can see how many amps the three posisitions of the heater fan draw.  And it tells me the general charge statof the battery by how quickly it drops down to minimal charge after starting the car.  My volt gauge basically sits there at 6.7 volts when the engine is running.  Maybe I am just better of reading between the lines.

Can't disagree.

My training was in racing and one thing you learn is that if you put a gauge in a car it really has to have a critical function. Another thing is the more gauges you need the more marginal the car. The last car I built had no tach, no oil pressure gauge and no temp gauge. Only an idiot light to energize the alternator. The driver (if he's doing his job) hasn't time to be pondering over gauges. Round "steam gauges" are usually turned in place so that the needles all point straight up when things are normal for that reason.

On a street car, if it has a gauge, I prefer that it works properly as expected. Most do not. The error of speedometers from the factory is considered "commercially acceptable" with + or - 2 mph (Commercially Acceptable is a General Motors term for "we're not going to fix it"). In fact as a kid I remembered reading magazine road tests which included speedometer error as a test criteria. Knowing what the error is could be helpful, that's why I spent so much time at the speedo shop interrogating the techs.

Speedometers are easy to check now days as most GPS units have a speed indicator. Tachometers require a trip to the speedo shop (you'd be shocked to know they operate on a curve and can be off wildly at different RPM. They usually are set accurately for idle and red line, everything else is "relative") Temp gauges can be compared with other known good gauges as with oil pressure gauges. Fuel gauges can be wired up and checked on the bench but that's a lot of trouble and only gets done when you know somethings wrong.