You have a wiring problem!
Take a careful look at the installation instructions. A OL and this is direct from the instructions is "Prodigy P2 “sees” an overload condition during operation."
A SH also direct from instructions is" 1. Brake wire sees short during idle condition.
2. Use of some test lights or non-Tekonsha testers
can cause this problem."
Because of the way a PWM inertia proportional device works cheap voltmeters do not give accurate readings.
As you will be advised to do you can junk the Prodigy and install a Max Brake then after spending big bucks you can fix the wiring problem so the Max Brake will work.
The P2 does have a limited Lifetime Warranty. Suggest you look it up on their website and you will see they offer the best warranty in the business. Even the Max Brake does not offer a lifetime warranty.