Tail/running lights both out at once, don't seem to be any of the usual problems. Suggestions?

There's a brake light switch under the dash.

Do you have any lights in the back? When your headlights are on?

SM-N900P ?

 

Assuming you performed all of the above and the lights are still out, I'd go with checking the brake switch, as previously mentioned.

 

"Taillights" are not the same as "brake lights". Assuming the OP is referring to the former (which is probably the case since he was traveling at 75 mph) and not the latter, then the brake light switch has nothing to do with their operation.

The former is an incandescent bulb while the latter is composed of six LEDs at the top of the light fixture. The former turns on when the light switch is turned to the "parking" or "headlight" positions while the latter turns on when the brake pedal is depressed.

I suggest the OP inspect the wiring harnesses that lead to the taillight assemblies, find the wires that connect to body ground back in that area, and verify the tightness of the hardware connecting the wires to the body. It may be necessary to remove some of the plastic hatch trim for access.

 

True enough. Sounds like the "tail" lights (LEDs). He should also check the stalk switch for the head/tail lights (I don't have an '08, so I'm assuming the light switch is on a stalk.)

 

Tail lights are incandescent. TAIL10A fuse provides power to the rear tail lights, the license plate lights, and the glove box light, and the front side marker lights.

See if they are all on and just your tails are out or if they are all off when in HEADLIGHT.

If all off then 12 volt is provided to TAIL 10 amp fuse by T-LP relay. That relay is controlled by BODY ECU and that ECU is commanded by the Stalk Combo Switch on the steering wheel. The headlight switch. So if all off:

Stalk Switch
Body ECU
Associated wiring and or ground points

I doubt its that relay or ECU though because that relay also powers PANEL7.5 fuse which powers the hazards and the mfd illumination you would notice if no 12 to PANEL7.5 fuse. That and the Body ECU controls a shitload of stuff and if out you'd be in deep dookey.
12 volt to both PANEL and TAIL fuses comes from relay T-LP.
No PANEL fuse & the mfd would not dim in the dark and no shift lever light and hazard illumination.

So if just tails are out your looking at the wiring after TAIL10 fuse.

Ground associated for the tails is located in the hatch well located right behind the license plate,
it's a white/black wire.
Power to tails come through only one junction connector J31 which looks like its up high near the drivers side rear tails high on the quarter panel behind the carpet. Has 4 brown wires on it all in parallel in that connector.
I would check for 12 with dc meter on any of those brown wires to ground with headlights on.

I have to mention alot of weird issues like this are sometimes caused by rodent infestation and wire damage from them chewing on wires. Lots of those posts. They find the wiring in a Prius delicious. That and car wreck and repair in the rear.
Which the posters never mentioned till after 20 questions.

Is the car garaged or outside?
Take out the cabin filter real quick and see if any rodent evidence like there trying to set up a bedroom.

Good Luck.

 

Mine were intermittent (might have be originals), needing a 'waggle.' As it is coming up to autumn, I thought I would give them a clean. When I did, strangely both of them immediately blew. New ones seem to work fine.