If you need to check the thermistor, here is the plug map:
Holding the plug vertically with the cord going down and looking at the connection points. 1 is top left, 2 is top right, 3 is second down left and so on with 9 being lower left and 10 being lower right.
1) Black - Power to cell
2) White - Power to cell
3) Black - Power to cell
4) White - Power to cell
5) Brown - Not used
6) Red - Goes to thermistor
7) Orange - Not used
8) Yellow - Not used
9) Green - Not used
10) Blue - Goes to thermistor
The display will show cold at 50 Fahrenheit which corresponds to a resistance of about 19,900 ohms. If you put your multimeter test leads on points 6 and 10, the resistance should correspond to the thermistor's temperature as shown in a 10 k thermistor chart.
50 f = 19,900 ohms
60 f = 15,310 ohms
70 f = 11,882 ohms
77 f = 10,000 ohms (the 10k reference point)
80 f = 9,297 ohms
90 f = 7,333 ohms
100 f = 5,827 ohms
110 f = 4,664 ohms
120 f = 3,758 ohms
130 f = 3,049 ohms
Note that each 10 k thermistor has its own specific chart, so the numbers won't be exact unless you have the chart for the specific thermistor.
If the thermistor is bad, then the salt reading will be off. Check the thermistor reading with a good ohmmeter.
You can tell the age of the cell by the first 4 of the cell serial number. For example, a serial number starting with 3E13 would have a 3 year warranty, E means cell and 13 means the cell was manufactured in 2013.