[Mgs] Fuel smell in boot/trunk

Sun Apr 19 17:29:38 MDT 2015

Paul,

Thanks for this info; you make it clear.   We kneed to archive this.

CR

On 4/18/2015 10:30 AM, PaulHunt73 via Mgs wrote:
> The MGA and MGB Jaeger gauges use a completely different method of 
> voltage regulation to the MGB Smiths gauges, and the system voltage 
> can vary significantly on both types - albeit a little less with 
> alternators. Effectively the earlier system uses a Wheatstone Bridge, 
> which is where with three known resistances you can arrange for a 
> voltmeter to display the resistance of a fourth unknown resistance, 
> and this is independent of supply voltage.  The three known 
> resistances are in the fuel gauge (two being magnetic coils), and the 
> unknown is the tank sender of course.
>
> MGB Smiths gauges use a thermal voltage stabiliser which outputs an 
> average of 10v over time regardless of system voltage, and thermal 
> gauges, both using heating coils wrapped round bi-metal strips.  
> Despite being called a 'stabiliser' the factory stabiliser is actually 
> switching system voltage on and off about once per second, once the 
> ignition has been on for a few seconds. At high system voltages you 
> get a relatively short 'on' time compared to the 'off' time, and at 
> low system voltage you get a longer 'on' time, always averaging about 
> 10v.  The tank sender simply varies the current through the gauge 
> heating coils. Because the gauges are thermal they are very slow 
> acting which means unless you look very carefully you can't see the 
> pointer moving as the voltage goes on and off.
>
> PaulH.
>
>
> ----- Original Message -----
>> From looking at the wiring diagram of the MGA I see that it doesn't 
>> have a voltage stabilizer to feed the gas gauge & sender;  it depends 
>> on the output voltage (V) of a terminal on the control box. 
>
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