25-04-2021, 08:51 PM
(This post was last modified: 25-04-2021, 08:56 PM by John Cornforth.)
Hi JonE
I have now had time to delve into this. Assuming you don't want to change or modify your early "minimum resistance when full" sender, these are your options:.
Stick a reminder label on the gauge that Full=Empty and Vice Versa
Find a matching early Gauge.
Run a late Gauge with the battery connected to G (the shell) and earth connected to B. Tank sender stays on T. You would have to insulate the gauge shell from the dashboard, or modify it to remove the internal connection to its shell and bring the battery feed out separately. Although the gauge will now read in the correct sense, the scale will be cramped up at one end. The cramping is because the two coils have different numbers of turns to balance their effect on the needle, and running the gauge "backwards" means that the coil with more turns is in the "wrong" circuit position and has an unwanted dominant effect.
Modify a late Gauge internally by swapping the physical locations of the two coils from one side to the other, whilst preserving their electrical connections. You might need to extend the coil tails so that they reach, and it's a fiddly job with fine wires. Each coil is held in with a single tiny stud and nut in the backshell, and these are slotted for calibration. I'd suggest just putting them in the centre of the slot to start with.
Disclaimer (!) I present this in good faith, but have not tried the above myself. If you do experiment, please fit a temporary 1 amp fuse in the battery supply in case of errors. These gauges normally draw something between 140 and 360 mA at 6 volts.
The following methods suggested over the years (it's not a new problem!) will NOT work:
Changing battery polarity
Wiring the sender the other way round and insulating it from the tank
Fitting resistors in various places
I have now had time to delve into this. Assuming you don't want to change or modify your early "minimum resistance when full" sender, these are your options:.
Stick a reminder label on the gauge that Full=Empty and Vice Versa
Find a matching early Gauge.
Run a late Gauge with the battery connected to G (the shell) and earth connected to B. Tank sender stays on T. You would have to insulate the gauge shell from the dashboard, or modify it to remove the internal connection to its shell and bring the battery feed out separately. Although the gauge will now read in the correct sense, the scale will be cramped up at one end. The cramping is because the two coils have different numbers of turns to balance their effect on the needle, and running the gauge "backwards" means that the coil with more turns is in the "wrong" circuit position and has an unwanted dominant effect.
Modify a late Gauge internally by swapping the physical locations of the two coils from one side to the other, whilst preserving their electrical connections. You might need to extend the coil tails so that they reach, and it's a fiddly job with fine wires. Each coil is held in with a single tiny stud and nut in the backshell, and these are slotted for calibration. I'd suggest just putting them in the centre of the slot to start with.
Disclaimer (!) I present this in good faith, but have not tried the above myself. If you do experiment, please fit a temporary 1 amp fuse in the battery supply in case of errors. These gauges normally draw something between 140 and 360 mA at 6 volts.
The following methods suggested over the years (it's not a new problem!) will NOT work:
Changing battery polarity
Wiring the sender the other way round and insulating it from the tank
Fitting resistors in various places