Converting an SP310 fuel sender to drive a late model gauge.
Posted: Sun Feb 02, 2014 11:13 pm
The SP310 not only is positive ground but the fuel sender characteristics are the exact opposite to what the late model and negative ground cars require.
My car had an aftermarket fuel gauge in it so I procured a genuine replacement which of course was meant for a negative ground car.
Result, gauge worked but back to front and it was also reading high since it was getting the full 12V signal instead of the reduced voltage from the instrument voltage regulator, not fitted to the positive ground cars.
So, here is how I modified the fuel sender to produce the required characteristics: -
So here we have a view of the rheostat housing. The float contacts are at the top of the resistor coil which is also where the coil wire connects to the terminal i.e. minimum resistance.
I have un-soldered and carefully lifted the wire from the coil off the screw terminal that feeds the gauge.
The coil just slides out and I have re-inserted it so the coil wire is at the bottom of the picture.
I used a short length of rigid copper wire to extend the sender terminal to the fine wire from the coil.
I slipped a short length of insulation over the rigid wire and soldered it to the coil wire. After cleaning and polishing all the internal electrical contacts, the float sender now reads 7.7ohm at FULL......
....and 86.4ohm for EMPTY.
This compares favorably with the characteristics of the later model senders which are 10 and 84 ohms respectively.
I also needed to insert a trimming resistor in series with the sender to reduce the gauge voltage to 8V.
A 39ohm resistor calibrates the gauge to read E when the float arm is fully extended.
I'm not too concerned about the gauge reading above F when the tank is full.
Job done!
My car had an aftermarket fuel gauge in it so I procured a genuine replacement which of course was meant for a negative ground car.
Result, gauge worked but back to front and it was also reading high since it was getting the full 12V signal instead of the reduced voltage from the instrument voltage regulator, not fitted to the positive ground cars.
So, here is how I modified the fuel sender to produce the required characteristics: -
So here we have a view of the rheostat housing. The float contacts are at the top of the resistor coil which is also where the coil wire connects to the terminal i.e. minimum resistance.
I have un-soldered and carefully lifted the wire from the coil off the screw terminal that feeds the gauge.
The coil just slides out and I have re-inserted it so the coil wire is at the bottom of the picture.
I used a short length of rigid copper wire to extend the sender terminal to the fine wire from the coil.
I slipped a short length of insulation over the rigid wire and soldered it to the coil wire. After cleaning and polishing all the internal electrical contacts, the float sender now reads 7.7ohm at FULL......
....and 86.4ohm for EMPTY.
This compares favorably with the characteristics of the later model senders which are 10 and 84 ohms respectively.
I also needed to insert a trimming resistor in series with the sender to reduce the gauge voltage to 8V.
A 39ohm resistor calibrates the gauge to read E when the float arm is fully extended.
I'm not too concerned about the gauge reading above F when the tank is full.
Job done!
