6200FE seems as a good wire - it is 16 gauge as the ones you are using, it has a shield and a drain wire, has nice capacitance and low resistance, maximum operating voltage is 300 V RMS, so it is OK for car applications, can take 6 A of current it can be used for the signal AND power...

Now, you need to see if you can find a seller who sells this in small quantities, as the cable is commercial...