2012 Prius V all kind of wrong

I have a 2012 Prius V with 50k miles on it. Never given me a days trouble and been perfectly maintained.

Wife wanted me to add a seat heater to it so I stripped down the seat and added the seat heater. I ground it to the frame and spliced into the hot wired for the lumbar support. Seat heater works, lumbar works...car won't work!
I had the battery disconnected the whole time I was doing this, about 5 hours, and reconnected it but the lights all come on, including fault with hybrid system warning light. When I try to shift into gear it won't and flashes up the PARK symbol. I've checked the fuses and they are fine and I've disconnected the battery a few times, negative and positive. I've also disconnected the orange safety key in the trunk and reconnected.

I've since cut the ground and taken the fuse out of the heater wiring harness but still having same issues. Lots of warning lights and won't start and won't go into D or R and tells me to put the car in park.

What the heck is going on with this thing?

 

It has an inline fuse and I’ve taken that out and cut off the ground wire to the accessory. Still having the same issue though.

 

Sorry, guys. What’s MG1 and HV traction pack mean?

 

Thanks for explaining.

It still gives me the same series of warning lights: ABS, Traction, oil, hybrid system and a couple of others. I hooked it up to a OBD2 and it shows no codes but it still won’t give me a ready. I’m completely baffled and trying to avoid having it towed to a dealer so they can charge me an arm and a leg for something that is probably an easy fix.
Thanks for tour help

 

I left the positive battery lead off overnight and still no change. Can’t for the life of me figure out what can be causing this.

Any ideas?

I feel like I need to do a reset on the ECU but I can’t find out how to do that.

 

Thank you for your message.
This is a daily driver and the battery I disconnected was in the right side of the trunk. The battery was never removed from the car.
I have tried several times to start the car/get it to go to ready and the same result each time. I've also left the ignition on for 10 minutes and still no change.
The battery is showing 12.05v under no load and it is the original battery, 6 years/52k miles.
I did remove the HV plug by mistake before I disconnected the battery and again just to check it while the battery was disconnected.
I had the negative (black) wire off the 12v battery while I was working on it and not the positive (red) wire. I did disconnect the red and the black for a while to see if that made a difference and it didn't.
Here is a screenshot of what I'm showing on the dash.
When I try to put it in drive or reverse, it tells me to put it back in park, this is probably because it has not gone into ready. This car has never given me a moments problem so I'm stumped.
I've worked on cars all my life so I'm pretty good at working on them but I've never worked on a hybrid.
As a side note, my 100k/72 month warranty expired 3 months ago and I had 2 months after expiry to get my money back.
Thanks for any advice.

 

Thanks. I feel good about the orange safety plug being in all the way but I'm beginning to wonder if the original factory 12v battery may need replacing.

 

I just remembered, I think I ran the seat heater for several minutes to test it before starting the car and after I had it disconnected for 6 hours. I bet I killed it.
Buying a new Toyota brand battery, made by interstate.