WTF

Did you check the condition of the internal fuses, and put a battery in it ?

 

try setting the dial to 20volts. it think that should give you a reading.

 

Get a new 1 1/2 V battery and see what shows. If not 1 1/2, take it back....easy enough.

 

If the internal fuse is blown, the meter display may still work, but the probes will be (internally) disconnected from the functional bits (or it may just be broken )

 

Put it on one of the resistance settings and touch the leads together, you should see close to zero ohms. This will tell you if the leads are good and at least the ohm meter is working. Then try a quick test on a 1.5v battery. If none of this works, then check the fuse.

 

I think the 3rd poster was correct. Set the dial to the 20v setting. It may not be sensitive/accurate enough to record low ( battery 12-13 voltage) on the 200v scale.

Good luck

 

Did you check to see if the meter is working at all? Touch the leads to the + and - directly on the car battery, with meter set on 20 as suggested. If you get no reading, then there is something wrong with the meter. If you get a reading on the meter at the battery but not at the gauges, then that's relevant.

 

This (or even a lower range setting if you are trying to get voltages from IC components / circuit board locations ----- they will typically be a helluva lot less than battery voltage of 12V, and some of them may even be AC rather than DC).

And, if your meter came with an instruction manual, it may be worth your time to read it .

 

the potential difference between the two leads on the gauge is going to be based on the resistance. Or in other words the voltage measured between them will be small as the gauge is known as a D'Arsonval ammeter. The sensor sending the signal is grounded to the chassis and varies the ground via resistance which in turn the gauge is displaying. To measure the voltage find a ground on the body, then measure at the leads, you'll find a small difference between each depending on the sensitivity of the meter.

 

There would be some kind of voltage regulator in the circuit which prevents readings changing with battery voltage.
On older cars a digital meter would not be able to measure the gauge voltages because they used crude bi-metal strip voltage regulators which outputted pulses. The 355 would not use this but maybe Veglia used a semiconductor device which creates pulses. Not come across this but it would explain why you are not getting a reading.

 

Andy,

He has stated that he is measuring with reference to absolute (chassis) ground, however. Assuming he is doing that correctly and actually has the other probe on a true chassis ground point, then the meter should be (at the very least) reading and displaying nominal battery voltage (or whatever the power supply voltage is within the circuit) as an "absolute" relative to ground regardless of whether or not "gauge voltages" are present at the test points ----- would you not agree ?

 

This would not be the case on the old fashioned system using a mechanical voltage regulator. The 12 volts is fed into the regulator which outputs pulses, then through the gauge, then through the NTC thermistor , to ground. Measuring at any point other than the 12V feed results in pulses which a digital meter would not display.

But thinking about this some more I think its highly unlikely that the system uses pulsed voltage. I think there should be a varying voltage on the sensor wire as expected and that there is some problem with the measurement , probes not contacting properly or incorrect ground point etc. On a conventional system the voltage should vary from about 3 volts when cold to 1 volt when hot.

 

Which is why you have it set on 200 volts.

For the third time, set it to 20.

Matt

 

Not familiar with the wiring here, but is there a pin on the connector which goes to both the oil pressure gauge and the temp gauge (12v feed)? Presumably that has 12 volts on it as the temp is working.
The oil pressure gauge has a red warning light which is not lit either so it seems to be no 12 volt supply to the gauge.

 

Ferrari use a VDO oil pressure sender which must have the case grounded to work properly. But I think you should still get a voltage at the connector, and I'll post a schematic of that circuit if I can find one.

 

Here's the schematic. I thought you'd probably see "some" voltage at the "G" terminal of the harness, with or without the sender connected, but I may be wrong. The sender is connected in the path to earth from the gauge.

One way you can tell if things are working or not is to leave the harness lead disconnected that would normally go to the sender terminal "G". That should give you a max reading on the gauge, then earth that same contact and the gauge should go to minimum.
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Steve ---

Another consideration is that Italian cars are nearly as notorious as British cars for having poor / infrequent chassis ground paths ---- even paths through the wiring harness can be inadequate (often the "fault", by the way ).

Whenever I do electrical checks on these cars, I am in the habit of connecting my "negative" probe directly to the negative battery terminal to ensure that I am tapped into a "true reference ground". For convenience, I usually connect a long jumper cable to the negative battery terminal so that I can run the other end of it close by to whatever location on the car I am testing. I would STRONGLY recommend doing this for your measurements.

 

umm the 355 isn't exactly wired like that really nice schematic John posted. I'll have to do a screen shot of the schematic but the gauge is tied in to the circuit board for the dash display. after the fun tonight I'll get it..