The new sender may be the wrong part. Screw terminals are not correct, photos below.
A '56 Temp sender (and gauge) are 'one year only' parts and don't match anything else.
They look like a '55 sender but are made for 12 volts. Part number 10884-B, at this link...
https://www.classictbird.com/Temp-Se...ctinfo/10884B/
Having one wire on the sender from the gauge is correct. The double terminal is a left-over design from some Flathead engines that had two temp sensors. See this link...
https://www.google.com/search?q=ford...OCESr8M:&vet=1
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