Tail light trouble

Rare question on this site.

Answer these.

Is the car a salvage title?
Do you park the car outside and see signs of rodents?

Mice love to chew on Prius wire. Take the cabin ac filter out see if any mice activity. If no rodent evidence got to be the relay.

 

I had trouble with my tail lights on my Prius from the time it was new. It was a bulb burnt out or a bad connection at the bulb housing.

Yours may be different, inspect the bulb housing and make sure it is clean and doesn't have any green stuff on it. Don't spread the connection where the bulb sets while troubleshooting.

Do you brake lights work? I'm thinking the tail and brake like share a common ground.

 

Was going to mention that but op says they went out together and has a voltmeter. That’s rare on this site lol.
But could have rotten sockets on both sides. Mine have been perfect but have been lubricated early in its life.

 

The license plate lights are usually tied into the tail lights but not positive on your Prius.

 

Sits out is all they need. Spend 10 minutes and look around. In the spare tire hatch in the cabin filter
In the engine air cleaner housing. Mice damage is very common on a Prius.

The relay is in the black plastic fuse box in the engine compartment on the right. Same box that has the battery jump points. Make sure all relays are seated.
Can’t find my Prius manual right now misplaced it or would tell you which one it is. Says it on the cover though.

 

When I rebulbed the whole car I put grease in the sockets. Prevents galvanization. I use 100% Ester synthetic wheel bearing grease. Hi temp stuff. Do not use Dino grease in a few years it will corrode.

 

A basic test light is a great tool for troubleshooting lights, it's what the truckers use.