Land rover voltmeter - what am I doing wrong!

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dag019

dag019

Well-Known Member
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Location
Warwick
First of all many thanks to @Hicap phill for the voltmeter to finish my dash for my rebuild after the fire I can now put the dash and centre console all back together.

I had a bit of a play with it this morning to work out how to wire it in and in testing the needle goes off the scale on the gauge. What am I doing wrong?

upload_2023-2-16_10-29-35.png


From this thread: link and from my testing I agree that the two terminal labeled 1 is for earth and 2 is for the 12v feed this would be ignition fed in the vehicle but for testing is direct to the battery. (both of mine are now male spade connections as one was broken and I have screw on male spaded on the shelf to repair but this should make no difference)

I have a 12 volt battery for bench testing that is 12.5 volts according to the multimeter.

upload_2023-2-16_10-30-16.png


From the way my old gauge worked I would expect 12.5V to be just under the central line as this is where it used to sit with the ignition on but no engine running, when running with the alternator power the gauge would then move to just over the centre line. However when connected to my test battery the gauge moves off the scale, see the video below:


 

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Your multi reads the voltage and that is 12.5, so unless there is something different in the [ think I am correct] 300 dash loom you are using can see no other reason.
 
I have been trying to sort out why the oil temp gauge does not work for too long.
All the parts test as they should, continuity, I need to look at it again.
But you have a voltmeter, trucks I have do not have voltmeter.
 
dag019 said:
First of all many thanks to @Hicap phill for the voltmeter to finish my dash for my rebuild after the fire I can now put the dash and centre console all back together.

I had a bit of a play with it this morning to work out how to wire it in and in testing the needle goes off the scale on the gauge. What am I doing wrong?

View attachment 283098

From this thread: link and from my testing I agree that the two terminal labeled 1 is for earth and 2 is for the 12v feed this would be ignition fed in the vehicle but for testing is direct to the battery. (both of mine are now male spade connections as one was broken and I have screw on male spaded on the shelf to repair but this should make no difference)

I have a 12 volt battery for bench testing that is 12.5 volts according to the multimeter.

View attachment 283099

From the way my old gauge worked I would expect 12.5V to be just under the central line as this is where it used to sit with the ignition on but no engine running, when running with the alternator power the gauge would then move to just over the centre line. However when connected to my test battery the gauge moves off the scale, see the video below:


Click to expand...


Probably a 6 volt gauge.
 
dag019 said:
If the consensus is that this one is not going to work and/or is not reparable that would be very much appreciated.
Click to expand...

Searched all over for it and had no luck. Found the fuel gauge and speedometer I took out, thought it was with them. Doubting if there even was one now (was about 14 years ago I rebuilt it all).
 
steve24v said:
Searched all over for it and had no luck. Found the fuel gauge and speedometer I took out, thought it was with them. Doubting if there even was one now (was about 14 years ago I rebuilt it all).
Click to expand...
Not a problem, many thanks for looking. I don't think it was fitted to all, and proper land rover ones seem to be very very expensive. I am looking at a durite one to match my rev counter but would rather have the original land rover if I can find one a t a sensible price.

freelance said:
what happens if you swap the wiring?
Click to expand...

If the wiring is swapped around the dial moves in the other direction which form my research is correct.
 
It's a VOLTMETER - regardless of how it's described by the parts book and most suppliers.

If nothing else, the terminals on its rear give away its function - it has a 6.3mm tab for its single 'live' connection.

An Ammeter (apart from having a different scale, and AMPS on its face) would have two large studs to be wired in series with the main battery to alternator cable, e.g. -

s-l1600.jpg

s-l1600.jpg
 
Sorry looked like centre zero ammeter. In that case its broken. I have had several ammeters with spade connectors on rear from old ammeters circa 1960's they were only 30-0-30

Just googled part number which led to Smiths web site and listed as 90-110 voltmeter, tried to find wiring diagram but it wasn't shown, but pointers to instrument pack were indicated. Perhaps it connected to a controller ( voltage stabiliser) like some fuel gauges. I think it may require detailed circuit diagram
 
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Just to finish this thread off I accepted the wisdom here that the gauge was just broken and set about "fixing" it. I acquired another land rover voltmeter that had the glass smashed and the green bulb holder broken off the housing. The voltmeter itself however was working. Some time spent carefully prizing the bezel off allowed me to remove the broken glass and extract the voltmeter itself. I then had to very very carefully repeat the process on the voltmeter that came from @Hicap phill (once again many thanks) to ensure I did not break this glass. I then put the working voltmeter in the dial housing that had the green illumination housing enact, refitted the glass and then again very carefully re-clamped the bezel down using a small punch.

I am not sure how good the seal will be from re-clamping it. The rubber gasket was intact and refitted correctly but I ma not sure if it would be worth very carefully applying a small seam of sealant around the bezel ring where it has been bent back over to meet the body. What are peoples opinion?

upload_2023-2-25_19-0-33-png.283559




Also looking at the voltmeter itself it is just a wire coil and some resistors unless I am missing something. What is likely to have failed in it to give the symptoms I had above and is it likely to be repairable or is it just not worth it?

upload_2023-2-25_19-0-16-png.283558
 
its most likely that one or both resistors have failed allowing the whole current to flow through the coil/meter. First step is to measure the resistors if you have access to a multimeter/ohm meter. If you cut one end off you can check the value against the code on the body of the component (the coloured rings) I can't see the colours on the pic but they are read from the opposite end to the gold or silver bands. The first 2n bands indicate a number and the 3rd band is the number of zero's.
Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, white=9 so if they were RED,RED,RED if would translate to 2200 ohms.
There is also a diode there the gray and black device this should only allow electricity to pass in 1 direction and and can be tested with ohmmeter there should be a high almost infinty or no reading in one direction and a low reading in the other direction. There also appears to be a strip of metal (a shunt) to allow most current to bypass the meter, check this is intact. The resistors or diode can be replaced but if the shunt is broken it will be almost impossible to reoair as I doubt there is a part number or value for it.
 
PaulJM said:
its most likely that one or both resistors have failed allowing the whole current to flow through the coil/meter. First step is to measure the resistors if you have access to a multimeter/ohm meter. If you cut one end off you can check the value against the code on the body of the component (the coloured rings) I can't see the colours on the pic but they are read from the opposite end to the gold or silver bands. The first 2n bands indicate a number and the 3rd band is the number of zero's.
Black=0, Brown=1, Red=2, Orange=3, Yellow=4, Green=5, Blue=6, Violet=7, Gray=8, white=9 so if they were RED,RED,RED if would translate to 2200 ohms.
There is also a diode there the gray and black device this should only allow electricity to pass in 1 direction and and can be tested with ohmmeter there should be a high almost infinty or no reading in one direction and a low reading in the other direction. There also appears to be a strip of metal (a shunt) to allow most current to bypass the meter, check this is intact. The resistors or diode can be replaced but if the shunt is broken it will be almost impossible to reoair as I doubt there is a part number or value for it.
Click to expand...

thank you. I will try testing the resistors. Looking at them I think they are:
Green, brown, black, gold = 51
Multi-meter reading = 50.1

Brown, red, brown, gold = 120
Multi-meter reading = 119.8

Do those figures sound correct?
also I am not that good with electronics how does having two different resistors in parallel like that work?

upload_2023-2-26_15-17-15.png


The grey black diode gives an error one way around and 7.85Mohms the other?

also you mentioned a shunt? Where are you seeing that on this? All I can obviously see based on your descriptions is the resistors and the diode. But I don’t know what I am looking for.
 
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Resistors in series just add up so Val1 + Val2 = Total
Parallel is the sum of reciprocals 1/Val1 + 1/Val2 = 1/Total

The last colour band (Gold = 5%) denotes the tolerance of the resistors. The measured resistance values seem fine to me.
 
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