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TR4 Fuel Gauge


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Help! Having successfully changed the positive to negative earth on my TR4a - charging correctly , swopped wires on the ampmeter so showing correct charge however the fuel and temp gauge are not registering. Tried changing wires on back of dials but no success. Can anyone out there help?

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Should make no difference as the gauges are only a wound resistor, With both gauges failing I would susspect a problem with the voltage stabiliser. Just the heat of a resistor opening and closing a contact. Unless its been changed to a modern solid state type when it will make a difference as I would expect it would be polaritiy sensitive.

Regards

Dale

 

PS Welcome to the forum :P

Edited by Dale  Moore
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The new solid state voltage stabilizers have polarity, and if yours is one of those, it will not work when you changed to negative earth. Just get a new one for negative earth. I did the opposite on my TR4 - changed it back to positive earth for originality, and the radio, the voltage stabilizer and the new solid state heater motor control all had to be adjusted/changed for this.

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I changed my 4 to negative earth and have no response from my temp or fuel gauge, the heater motor does not work either. I thought about the voltage stabiliser but it's early days in sorting out my electrics... So would a new solid state voltage regulator POSSIBLY sort these problems out?

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I had problems with my fuel and temperature gauges even with a replacement old style stabiliser. I changed that for a solid state one, bought via ebay, and they have been fine ever since.

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The fuel and temperature gauges on a TR4 or 4A are not sensitive to polarity, neither is the ammeter

The old style mechanical voltage regulator for the instruments is not sensitive to polarity

 

Solid state voltage regulators for the instruments are sensitive to polarity and will need to be changed to suit the cars polarity if it is changed

If the car has been fitted with a newer style voltmeter, these will be sensitive to polarity.

 

The reason for these differences are that the original gauges were either moving iron or hot wire which only measured the amount of current and not the direction in which it flowed.

Modern gauges use moving coil mechanisms which balance a current dependent turning moment against a spring. The turning moment is one direction for negative earth and the other direction for positive earth (looking at the front of the gauge), but of course the spring acts in the same direction and doesn't know about the direction of the current so one way will work and the other way won't.

 

I hope this hasn't completely confused you!!

 

TT

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In my experience, the ammeter needs to be reversed when changing polarity. The generator must also be repolarized, and the wires on the coil should be reversed. The fuel gauge and the temp gauge require no change. The early radios have a polarity switch which must be set to the new polarity.

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I cannot remember disagreeing with Tony Thomson on matters electrical before, but the Ammeter is a moving coil, centre zero, bi-directional device - it has to be in order to show charge and discharge.

Hence, when changing from positive to negative earth, the connections to the Ammeter MUST be reversed, else it will indicate discharge (negative) when it should be showing charge, and vice versa.

Ian Cornish

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Agree, I have already swapped my ammeter connection over and that works fine. The things that don't seem to work are the temp gauge, fuel gauge and heater fan (all connected to the voltage regulator). Do I need to swap the connections on the voltage regulator over...bearing in mind they are side specific and will need new spade connections?

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Temperature & fuel gauge received a (crudely) regulated supply of about 10 volts from the small box beneath the dashboard/bulkhead. As long as you are using the original type of regulator, then there's no need to swap anything - if it's a modern, electronic, unit, it is essential to get the polarity right.

 

Heater motor: Ian Brown (see article in latest TR Action) tells me he had to swap the connections to his TR3A's heater to get it to blow air into the cockpit, rather than suck it out! I imagine the same would be true for a TR4/4A, but it's easy enough to check. The same is true for any cooling fan, such as a Kenlowe.

 

Ian Cornish

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Heater motor: Ian Brown (see article in latest TR Action) tells me he had to swap the connections to his TR3A's heater to get it to blow air into the cockpit, rather than suck it out! I imagine the same would be true for a TR4/4A, but it's easy enough to check.

 

On my early 4 I did not have this problem and, as it sounds like others haven't (or at least haven't noticed ;-)), I am guessing any heater motor polarity sensitivity stopped at TR3A's.

 

But, as Ian says, it should be easy to check in each case.

Edited by TorontoTim
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Hi Grafton, when you say 'swapped the wires' on the voltage stabiliser do you mean you swapped the original configuration over - did you have to put new connections on? Mine is as original but now negative earth - should I swap the connections over? Thanks

 

Hi yes change the wires on the voltage stabiliser made up some adaptor leads to fit.Anyway the voltage stabiliser must have been faulty before as it was giving out low voltage ie under 6v not the correct 10v giveing me faulse reading on the gauges. Bought a new soild state one via ebay fitted it the other day everyting is now find .PS had no trouble with heater motor, regards Grafton

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Hi yes change the wires on the voltage stabiliser made up some adaptor leads to fit.Anyway the voltage stabiliser must have been faulty before as it was giving out low voltage ie under 6v not the correct 10v giveing me faulse reading on the gauges. Bought a new soild state one via ebay fitted it the other day everyting is now find .PS had no trouble with heater motor, regards Grafton

 

 

 

As it happens I have a heater motor on my bench.... which ever way round it's connected it rotates in the same direction.

 

 

Mike

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Hi yes change the wires on the voltage stabiliser made up some adaptor leads to fit.Anyway the voltage stabiliser must have been faulty before as it was giving out low voltage ie under 6v not the correct 10v giveing me faulse reading on the gauges. Bought a new soild state one via ebay fitted it the other day everyting is now find .PS had no trouble with heater motor, regards Grafton

 

 

 

As it happens I have a (TR4) heater motor on my bench.... which ever way round it's connected it rotates in the same direction.

 

 

Mike

Edited by MikeF
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