04 prius: night running light and tail light.

The tail lights are NOT real bright. Check the bulbs up front, they may be burned out. I recommend using Amazon.com: 2825ll Sylvania Long Life That is the equivalent to the OEM bulb and seems to work well on our Prius. Other's here on PC have also recommended using LED's. I have no information or recommendation concerning them.

Hope this helps you and "Welcome to Prius Chat!"

 

You can also buy those bulbs at any parts house. Amazon is just a reference point for that bulb.

 

Hmmm. Might be a bad ground. The harness is grounded in the back end. Look in between the storage tray (black box under floor) and the rear end inside the hatch. You will see the harness and the ground in the middle of the rear end under the removal floor in the hatch area once your remove the storage tray.

Also, previous owner might have fiddled with the bulbs, so you might want to check them also. Could be small LED's in there, but I am guessing at that point.

 

Check fuse #25, it's a 7.5 amp for daytime running lights. Could just be fuse burnt out. Those bulbs are easy to replace if it's the bulbs. I discovered mine were out several months ago and the fuse was actually missing. No idea where it went, but it fixed the problem.
Also check fuse #15 that is for Tail lights, license plates light, parking lights. Supposed to be 10 amp. The lamps for tail lights 2825 are also easy to replace. They do sometimes get dimmer as they age. When you see cars with one dimmer than other, they usually have replace just one that burned out. Replace both, they come in a two-pack anyway. Just hope the brake lights never go. Have to replace the entire tail light assembly for those.