variable voltage to energize relay

The truck is 12 volt and will have a fuel pump booster that is full time powered in by 12 volt when truck is on. The booster is activated by a Hall Switch based on boost. However, the variable voltage output will be 12 to 18 volts (hopefully closer to 18) is what I want to trigger a relay which will allow a SPDT relay to switch from the truck's stock Fuel Pump Control Module to the booster. Once out of boost the switch would return to stock control. Have not found relay that is variable 12 to 18 volts on the coil side or maybe there's a better way? Thanx Tomy

Either a 12V relay with a current limiting circuit, or a 12V switch (ie, switches on output when voltage exceeds 12V), or a comparator circuit (ditto).

Thanks for the reply. Looks like it starts to get more complicated and expensive with variable voltage, unless I am looking in the wrong places. Two other options I was contemplating: Putting a one way diode on the stock wire so when the booster kicks on it can't feedback to the stock controller...but was concerned about the diode potentially causing issues under normal operation long term...probably unfounded on my part. Or setting the booster to max perm. and bench testing the voltage to come up with a resistor to cut the voltage back to near 12 volts to power coil. And leaning toward this as the least risky. Input and ideas welcome.