How did you wire the new one? Do you have a voltage tester?

Left Cable

• Black wire: Line
• White wire: Load

Right Cable

• Black wire: Load
• White wire: Line

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1. Which cable goes to the power source and which cable goes to the heater?
2. What is the brand and model of the old thermostat?

Thanks guys. Sorry for the delay and appreciate the help. When attemting to answer your qurstions i decided to take a reading on everything Theres something strange going on with the wiring I'm measuring 75-80V on each wire.

"I'm measuring 75-80V on each wire."

You have to fix your vocabulary to make clear what you measured. A wire cannot contain a wire. A cable contains one or more wires.

1. Which pairs of wires did you test?
2. When you performed the tests the wires were disconnected from any thermostat, right?
3. What are the other ends of the left and right cables connected to?

Ok I have two Romex cables coming into the box both 2 wire(Black & White) with ground. I measured each individual wire with black probe to metal box and red probe to each wire. each measuring the voltage mentioned before.

I would measure the voltage (a) between the black and white wires in the left cable and (b) between the black and white wires in the right cable (with all wires disconnected from the existing thermostat).