New baseboard heater wiring

I purchased a new baseboard heater for a spare room (Dimplex LPC with built in therm). The old heater never worked so the wires were just closed off with nuts. I have 2 supply lines and confused as to which one to use for the install. I assume 1 is for a thermostat but both lines are cut just long enough for a heater on the floor. I have tried wiring each supply line and closing off the other with nuts, but I have no power to the heater. The instructions do say the connections must be made on the right side, but I am going on the left which does have a junction. Customer service for the company is non existent.