PO5947 Code Thermostat heater control circuit open

Looking for some help. I have a 2009 Aveo5, and last summer, I noticed the heat gauge was not working and last spring, I did not have much heat from the heater. I replaced the thermostat housing, and I now have good heat in a Minnesota winter and the temp gauge goes almost up to the half way mark, it is just 1 needle from the middle which is right where my 2006 - same model ran its temp gauge at when new. I have been getting a PO597 code which says it is the thermostat heater circuit open. I had the code checked and cleared about 5 times and the engine light is on and the code keeps coming back, but the car runs great. The engine light has came off and on a few times, but is now on all of the time. I have pulled the connector on the thermostat housing off and on a few times and it looks clean or at least not corroded. Does anyone have any ideas on what next or how to check it? Any help us much appreciated. Trying to figure this out since there is no money for a trip to the garage right now. I do have a multimeter.

I also had a battery draw a couple of months ago, and I hooked up my meter and started pulling fuses and the draw stopped when I pulled the fuse for the radio. Since then, no battery draw or radio and I am wondering if the radio had a short or???? I was thinking of hooking up the multimeter to the power leads going to the radio with the car off and see if I get a draw and thinking if not, it would be a short in the radio. I bought this car used and it looks like someone may have had another radio in it at one time. I say that because when I pulled the trim to fix the latch for the back hatch, I noticed that the factory wiring for the speakers were twisted together like we did when we were kids. It also has a 4" stainless aftermarket pipe on back, and at 56, it is not needed for me even though I build street rods. This is just a "get er" to work vehicle. Overall, it runs very good, it just needs the bugs worked out.

Thanks in advance for any ideas.

RJM