05-06-2023, 07:57 PM
Hi Russel
From what I can work out from photos, the mounting bracket has insulators where the two "hot" terminals pass through it. With these in place, there is no problem connecting it to ground via a metal dashboard. The body of the gauge would be similarly grounded. There is a separate ground terminal on the gauge body, and unless you can rely on a good ground via the metal dashboard (chancy) it is best to fit a dedicated ground wire. Testing on the bench you will definitely need a ground wire.
I suspect the operating principle is the "two coil moving iron" type, which will be familiar to anyone used to A7 petrol gauges. Response to sender resistance changes is rapid, unlike the later era thermal types.
I have no information on the correct sender resistance range for 6 volts, but a typical range for 12 volt USA gauges would be 240 ohms cold to 33 ohms hot. The best approach might be to try a number of different value electronics style resistors in place of the sender, which will tell you what resistance corresponds to what temperature reading. Low power resistors are fine, with the demise of Maplin you could source them from CPC or internet auction. Alternatively, use a 1000 ohm variable resistor ('pot'), adjust it for each temperature reading and check its resistance each time (out of circuit) with an ohmmeter.
In a similar way, your sender resistance can be checked with an ohmmeter, with the sender tip immersed in 100 deg C boiling water, 12 deg C cold tap water or some blend in between.
Armed with this information we will be in a better position to decide if a different sender is needed, or if your original can be persuaded to work.
From what I can work out from photos, the mounting bracket has insulators where the two "hot" terminals pass through it. With these in place, there is no problem connecting it to ground via a metal dashboard. The body of the gauge would be similarly grounded. There is a separate ground terminal on the gauge body, and unless you can rely on a good ground via the metal dashboard (chancy) it is best to fit a dedicated ground wire. Testing on the bench you will definitely need a ground wire.
I suspect the operating principle is the "two coil moving iron" type, which will be familiar to anyone used to A7 petrol gauges. Response to sender resistance changes is rapid, unlike the later era thermal types.
I have no information on the correct sender resistance range for 6 volts, but a typical range for 12 volt USA gauges would be 240 ohms cold to 33 ohms hot. The best approach might be to try a number of different value electronics style resistors in place of the sender, which will tell you what resistance corresponds to what temperature reading. Low power resistors are fine, with the demise of Maplin you could source them from CPC or internet auction. Alternatively, use a 1000 ohm variable resistor ('pot'), adjust it for each temperature reading and check its resistance each time (out of circuit) with an ohmmeter.
In a similar way, your sender resistance can be checked with an ohmmeter, with the sender tip immersed in 100 deg C boiling water, 12 deg C cold tap water or some blend in between.
Armed with this information we will be in a better position to decide if a different sender is needed, or if your original can be persuaded to work.