2005 Gen 2 - Left Taillight isn’t lighting after plastic shielding broke - Dealer or home fix?

Buy another one and do it yourself. It'll be half the cost of the dealer's diagnostics

 

Try this one...

TYC 2004-2005 Prius taillight assembly, left side. On Amazon

I believe you will still need the light bulbs for this assembly though.

 

If there's a chance u want to keep it, I would check the connection first. Also, make sure it's getting power from the car, a replacement won't work without that either. May be blowing fuses if water got in there.

 

I've cracked mine, left side of a 2008, too.
I bought an used original part from a Toyota dealer.
The assy comes without bulbs and without sockets (only with the brake LEDs).
It's easy to change from inside the trunk.
But I would recommend too, to check the electrics. While the right lights are on, the sockets of the left ones should have round about 12V (up to 13,4V to 13,8V in ready state). If not and if all fuses are okay, a new light assy wouldn't help you further.

 

I replaced the right taillight assembly of my 2007 a year ago. I agree that since the light sockets for the tail, turn and backup lights are not included, replacing the taillight assembly will help the physical damage issue but does nothing with respect to whether those lights actually work.

If all lights are not working, then it is possible that the connection to ground has a fault.