41 replies to this topic

[stevelane]

Well there are some other less intrusive things you could try before making the external voltage stabilizer conversion.  
 
First, try a mechanical inspection.  Shine a flashlight in the tank to see if the float is floating.  If it is not, you know there is a mechanical issue to sort out (binding arm, perforated float, etc).  
 
If the float appears to be floating, add some resistors to your Maplin order.  Buy a small quantity of 5%, 1/2 Watt resistors rated at 33 Ohms, 130 Ohms, and 240 Ohms (or close to these values).  These will be used to simulate the sending unit.  Disconnect the two wires at the sending unit.  With the ignition switch in the run position, insert the 240 Ohm resistor in the two wire terminals making sure the resistor leads are making good contact with the terminals.  The gauge should read close to empty but the needle should be up off its bottom position.  Replace the 240 Ohm resistor with a 130 Watt resistor.  After a few moments the fuel gauge should go somewhere near 1/2.  Finally try the 33 Ohm resistor.  The tank should read close to full but not be pegged all the way to the top.  If you don't get the empty-1/2-full results with these tests, repeat the tests by inserting the resistors in the green/black sending unit wire terminal and connecting the other resistor lead to a wire that you run directly to the battery (-) terminal.  If you get the correct empty-1/2-full results connected directly to the battery terminal, the black sending unit wire has an earth problem.  If neither test method makes the fuel gauge read correctly then you have cause to try the external voltage stabilizer conversion.

Should these be .6W resistors or 3W. I can get to maplins tomorrow to get them.

Really appreciate your help on this

[stevelane]

Sorry, read it again and answered my own question

[stevelane]

Well I bought the resistors and got exactly the same as I do with the sender.

With the highest resistance I got nothing, with the middle I got a slight twitch, and with the lowest resistance it went half way and stopped

This was the same when linked directly to the - terminal of the battery

Seems the external voltage stabiliser is my last option

[dklawson]

In an earlier post you said that shorting the two fuel sending unit wires together made the gas gauge work but I don't remember you saying how high the fuel gauge reads when you short the two wires together.  Did it go all the way past full?  You have not carried out a similar test on the temperature gauge have you?  My reason for focusing on both gauges and all these tests is that BOTH gauges are powered by the voltage stabilizer.  If both gauges are not showing the same behavior (reading low in this case) then the problem is not likely to be with the voltage stabilizer.  

 

You can earth the green/blue temperature sending unit wire and turn on the ignition to test the temperature gauge.  If the gauge goes above HOT, that says the gauge and voltage stabilizer are working.  If I failed to mention it earlier, the mid ("N") portion of the temperature gauge should be close to about 185 oF (85 oC).  If your temperature gauge reads low when you short its sending unit wire to earth or if the needle appears to be indicating lower temperatures than those measured at the thermostat housing, top hose, and radiator header tank... then the stabilizer is probably bad and needs replacement (or bypass as described in the FAQ article).  

 

Again, if the temperature gauge appears to be accurate and the fuel sending unit(s) work the way they are supposed to, this suggests a problem with the fuel gauge itself and not with the voltage stabilizer.  I would just hate to see you go through all this effort only to find the problem was not where you thought it was.

[stevelane]

In an earlier post you said that shorting the two fuel sending unit wires together made the gas gauge work but I don't remember you saying how high the fuel gauge reads when you short the two wires together.  Did it go all the way past full?  You have not carried out a similar test on the temperature gauge have you?  My reason for focusing on both gauges and all these tests is that BOTH gauges are powered by the voltage stabilizer.  If both gauges are not showing the same behavior (reading low in this case) then the problem is not likely to be with the voltage stabilizer.  

 

You can earth the green/blue temperature sending unit wire and turn on the ignition to test the temperature gauge.  If the gauge goes above HOT, that says the gauge and voltage stabilizer are working.  If I failed to mention it earlier, the mid ("N") portion of the temperature gauge should be close to about 185 oF (85 oC).  If your temperature gauge reads low when you short its sending unit wire to earth or if the needle appears to be indicating lower temperatures than those measured at the thermostat housing, top hose, and radiator header tank... then the stabilizer is probably bad and needs replacement (or bypass as described in the FAQ article).  

 

Again, if the temperature gauge appears to be accurate and the fuel sending unit(s) work the way they are supposed to, this suggests a problem with the fuel gauge itself and not with the voltage stabilizer.  I would just hate to see you go through all this effort only to find the problem was not where you thought it was.

 

Well I've got onto the laptop now, I usually use my phone to update and this is why I keep missing stuff

 

I have put the external stabiliser together tonight. To be honest, it wasn't really putting me out as the dash has been off for two years and I an tackling this job before I put it back together so this wasn't as much effort as you may think.

 

However, it hasn't worked, I now get the same reading on the gauge, even when its not attached to the sender! Unfortunately my knowledge of what I am doing is zero so I have no idea whether or what I've done wrong.

 

I can easily undo this and go backward.

 

So to answer your other questions.

 

When I shorted the wires it went straight to the top and fast but I have never carried out a similar test on the temperature sender unit but I can do once I take a backward step and take off what I have done.

 

I think I am right by saying that the temp sender is the one that screws into the cylinder head? The only reason I ask is that there is no green/blue wire but a black one that comes from the same bunch of wires that goes to the alternator. However, this looks like it may have been replaced at some point but just wanted to check.

 

Now excuse my ignorance, but to earth this do I literally just join a wire to the sender and then clip to any earth anywhere?

 

Will take off the voltage stabiliser whilst I await your reply

 

Thank you again

[stevelane]

OK, so I have taken it off and put the gauges back to how they were.

 

I have shorted both to show how high they go and this is where they sit:

 

 

Attached Files

•  gauges.JPG   50.83K   22 downloads

[stevelane]

Can also confirm that I have also checked the sender is floating by a visual inspection in the tank and it is

[stevelane]

I may be clutching at straws but just trying to be logical here, but is it possible that my gauges and sender just aren't compatible with each other?

 

When I tried other senders they were all these minispares item:  XNB10007. I had avoided the other one that minispares had available was item XNB100380 because it was for injection cars which I don't have, but as I said before, I don't know if these gauges were fitted as standard.

 

The gauges I have are the Nippon Seiko ones but would they ever have been fitted as standard to a Mini City?

[dklawson]

Sorry if my posts are rather long-winded.  I believe if you understand how the system is supposed to work you will have more luck troubleshooting it.

 

The fuel sending units after 1964 until the end of production operated over the same resistance range.  This is nominally 30 or so Ohms for full to about 270 Ohms for empty.  That was true regardless of Smiths or Nippon Seiki gauges.

 

The temperature sending unit is the one that screws into the head and it is located near the thermostat housing.  You have identified it correctly regardless of the wire color.  (As a future note... black is a particularly bad choice for a replacement in Lucas wiring schemes.  Black is used for earth wires which this clearly is not).  Yes, to short it to earth you only need to connect it (directly or indirectly with a wire) to a bare metal spot on the engine block.

 

I have not had the opportunity to work with Nippon Seiki gauges but I expect their needles to go "above" the top mark when their sending unit wires are shorted to earth as that is what the Smiths gauges do.  Consider for a moment the case of the fuel gauge.  As I mentioned, the nominal fuel sender resistance for full is 30 Ohms.  When you earth the green/black sender wire, the resistance to earth goes to "0" (or pretty darn close).  Therefore, more current flows through the circuit and that makes the needle go "above" the highest mark on the gauge scale.  

 

You said that with the external voltage stabilizer connected to the flex circuit your gauges now read wrong even when the sending units are disconnected.  That says something is wrong but without seeing your gauge cluster up close I doubt I could tell you what is wrong. 

 

You cannot measure the output of a electromechanical voltage stabilizer (Smiths or Nippon Seiki) directly with a multimeter.  The unit switches on-and-off several times per second so there is a voltage continually swinging between 0V and 12V.  WIth the points in your Nippon Seiki voltage stabilizer held apart by tape and the external voltage regulator connected to the cluster you WILL be able to measure the voltage at various places to confirm you have wired the regulator correctly.  Specifically, turn the key to the run position AND disconnect BOTH sending unit wires and keep them from touching earth.  Use a multimeter to measure between the terminal on each disconnected wire's end and earth.  Each should measure 10V if you have wired the external voltage regulator correctly.

 

The following is a short explanation of what is supposed to happen with these gauges (both fuel and temperature).

You turn the key to the run position.  12V is supplied to the voltage stabilizer.  The stabilizer's job is to reduce that 12V in to a nominal, average 10V output.  The 10V output goes into one side of the gauge (either/both gauges).  Inside the gauge is a resistance wire wound around a bimetallic strip connected to the gauge needle.  The other end of the resistance wire is connected to the sending unit wire.  The far end of the sending unit wire is connected to the sending unit itself.  The sending unit is a variable resistor.  The other side of the sending unit provides an earth connection either directly by its mounting threads (temperature sender) or via a wire to earth (fuel sending unit).  Current flowing through the circuit causes the resistance wire wrapped around the bimetallic strip connected to the needle to heat up.  As that bimetallic element is heated it bends and moves the needle.  The sending unit "throttles" the flow of current and thus changes the amount of heat the bimetallic strip sees. 

 

So... if your gauges are moving up off zero with the external voltage regulator connected AND the sending unit wires are disconnected at the same time... something is seriously wrong with the circuit.  Again, I doubt I could tell you what is wrong without being there in person.

[stevelane]

Sorry if my posts are rather long-winded.  I believe if you understand how the system is supposed to work you will have more luck troubleshooting it.
 
The fuel sending units after 1964 until the end of production operated over the same resistance range.  This is nominally 30 or so Ohms for full to about 270 Ohms for empty.  That was true regardless of Smiths or Nippon Seiki gauges.
 
The temperature sending unit is the one that screws into the head and it is located near the thermostat housing.  You have identified it correctly regardless of the wire color.  (As a future note... black is a particularly bad choice for a replacement in Lucas wiring schemes.  Black is used for earth wires which this clearly is not).  Yes, to short it to earth you only need to connect it (directly or indirectly with a wire) to a bare metal spot on the engine block.
 
I have not had the opportunity to work with Nippon Seiki gauges but I expect their needles to go "above" the top mark when their sending unit wires are shorted to earth as that is what the Smiths gauges do.  Consider for a moment the case of the fuel gauge.  As I mentioned, the nominal fuel sender resistance for full is 30 Ohms.  When you earth the green/black sender wire, the resistance to earth goes to "0" (or pretty darn close).  Therefore, more current flows through the circuit and that makes the needle go "above" the highest mark on the gauge scale.  
 
You said that with the external voltage stabilizer connected to the flex circuit your gauges now read wrong even when the sending units are disconnected.  That says something is wrong but without seeing your gauge cluster up close I doubt I could tell you what is wrong. 
 
You cannot measure the output of a electromechanical voltage stabilizer (Smiths or Nippon Seiki) directly with a multimeter.  The unit switches on-and-off several times per second so there is a voltage continually swinging between 0V and 12V.  WIth the points in your Nippon Seiki voltage stabilizer held apart by tape and the external voltage regulator connected to the cluster you WILL be able to measure the voltage at various places to confirm you have wired the regulator correctly.  Specifically, turn the key to the run position AND disconnect BOTH sending unit wires and keep them from touching earth.  Use a multimeter to measure between the terminal on each disconnected wire's end and earth.  Each should measure 10V if you have wired the external voltage regulator correctly.
 
The following is a short explanation of what is supposed to happen with these gauges (both fuel and temperature).
You turn the key to the run position.  12V is supplied to the voltage stabilizer.  The stabilizer's job is to reduce that 12V in to a nominal, average 10V output.  The 10V output goes into one side of the gauge (either/both gauges).  Inside the gauge is a resistance wire wound around a bimetallic strip connected to the gauge needle.  The other end of the resistance wire is connected to the sending unit wire.  The far end of the sending unit wire is connected to the sending unit itself.  The sending unit is a variable resistor.  The other side of the sending unit provides an earth connection either directly by its mounting threads (temperature sender) or via a wire to earth (fuel sending unit).  Current flowing through the circuit causes the resistance wire wrapped around the bimetallic strip connected to the needle to heat up.  As that bimetallic element is heated it bends and moves the needle.  The sending unit "throttles" the flow of current and thus changes the amount of heat the bimetallic strip sees. 
 
So... if your gauges are moving up off zero with the external voltage regulator connected AND the sending unit wires are disconnected at the same time... something is seriously wrong with the circuit.  Again, I doubt I could tell you what is wrong without being there in person.

Please don't apologise for the length of your replies, you've been extremely helpful

It's getting late here so I've shut up shop for the day and will return to it tomorrow.

When I was using google I found a short thread on another forum that you had commented on where the guy was suggesting that's maplins had changed the output so I did wonder if this could have the effect that I got.

I'm also considering trying the different type of sender just to rule that out

[dklawson]

Steve, please do not feel you need to quote entire posts each time you reply.  It just reminds me how long my posts are.

 

I don't know that I ever suggested that Maplins had changed the specs on anything they sell.  The voltage regulator chips used in place of the voltage stabilizer are industry standard items so Maplins will not have been able to change anything except their supplier.  

 

I'm sure that as you work through this system methodically you will determine what is wrong and address it.

[stevelane]

You didn't suggest it, the other guy did, he had downloaded a PDF that informed him the ground and output were around a different way

[stevelane]

You didn't suggest it, the other guy did, he had downloaded a PDF that informed him the ground and output were around a different way

[stevelane]

Looks like I may have to admit defeat on this one, really need it in the road so will give up, put the dash back and come back to it later

[stevelane]

Made a minor breakthrough tonight!

 

I removed the sender and the gauge and attached them to a circuit with a spare battery that I had and success! Full range through the gauge as I lifted the float and returned when dropped!

 

At least I now know that the components of the circuit are working and this must be a wiring issue, now all I have to do is find out where!

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•  photogauge.JPG   70.34K   16 downloads