C1242, C1A50 in 2021 Prius after installing Aftermarket Alarm

Hi everyone, after learning so much from this forum for the last few months, I finally have a question of my own that doesn't seem to have a clear answer as of yet. Hoping to pick the brains of some gurus here...

Here's the history:

• 10/29 had an aftermarket alarm (Viper 5706V + GPS module) installed by an independent. All the alarm functions worked, but immediately upon driving the car, a whole host of brake warning messages came on. These include: PCS malfunction, antilock brake system malfunction, braking power low, PKSB malfunction. The brakes still worked just fine though.
• 10/30 discovered the alarm had completely drained the battery, had to manually unlock the car.
  
• 11/2 alarm was disconnected, battery charged. Driving the car, I noticed all the brake warning messages were still there, but they would mysteriously all disappear whenever I hit the brake pedal.
  
• 11/4 left the car to sit to confirm that the source of battery drain was eliminated.
• 11/7 battery was fine, so the alarm was re-installed with a new brain. Still, the brake warning messages persist, now constantly (even when pressing the brake pedal). The installers verified all the connections were properly made, and asked that I take it to a mechanic to further diagnose the problem, agreeing to cover additional costs. I cleared the codes with OBD2 but they came right back.
  
• After the installers left, I used my Techstream to clear the historical codes (from battery discharging and installation), but the two codes remain: C1242, C1A50.

Here's the current state of the vehicle, in case the history may contain somewhat irrelevant info:

• Upon starting the car, brake warning messages are: PCS malfunction, antilock brake system malfunction, braking power low, PKSB malfunction. These warnings persist even if brake pedal is depressed.
  
• Check engine light on with codes C1242, C1A50
• Brake power and braking works as before and feels the same as before in terms of power and regeneration. Still getting 50+ mpg. Parking brake also works.
  
• Techstream screenshots are below:

To elaborate on the screenshots:

• C1242 detail: open circuit in IG1/IG2 power source circuit
• C1A50 detail: brake system malfunction
• I ran a CAN bus check and verified that all the communications are normal and working. This was to rule out the possibility that the alarm installers may have left a harness unplugged.

Can anyone provide any insight on what may be causing my two error codes along with all the brake warning problems? I am prepared to bring it in to the dealer, but for my own learning, I would love to explore some DIY options. I am reasonably well versed in electronics and wrench-turning, and have my own (cracked) Techstream I bought off of Amazon (which by the way is a really helpful tool).

Thanks for looking!

 

Uploading the pictures here as it looks like my image uploads failed...