Rear Lights out, but a knock brings it back???

Hmm, That's a good one. I would have said a loose ground. And since it's on both sides and not the ground, maybe you have a bad trailer hitch module? I'm assuming you checked the ground coming off of the module, too...

Have you had the wiring kit in for awhile? It may be worthwhile to check it with a volt meter (or even a 12v light) to see that it's operating as expected.. In the trailer wiring harness, the running lights goes to the trailer through the wire that is right next to the ground. Sorry, can't remember what color that is.

Looking at the Prius wiring diagram, the brown wires that feed the tail lights run uninterrupted all the way from the junction box that holds the fuse.... It's gotta be something out back between the brown wires coming in on the fuse side of trailer wiring harness to ground which is the bolt on the inboard side of the bumper.... I'm sure you saw this one when you put the wiring harness in. It's also shown on EVnut's site as this is what he grounded his module to.

Good luck,

 

Definitely check the ground connections.. I had an old Tercel where the dealer would always call me to tell me that I had bulbs out (and that they'd be happy to replace them for me at $10 a bulb and $25 labour).. I always turned them down, then went home and tightened the ground wire nut in the tail light assembly, and the lights would be fine.. I had the same problem in a Corolla and it was always the dealer who "found" this condition, so I suspect that they deliberately loosened the ground nuts every time..

 

<div class='quotetop'>QUOTE(efusco @ Apr 26 2007, 02:14 PM) [snapback]430769[/snapback]</div>

A tap with an intermittent connection is a definite possibility. I've been having flakiness problems with my CAN-View, and finally confirmed that the problem was with the 12V tap. I changed to a different 12V source (in the center console), and it went from not working at all (that and the NAV) to working perfectly (keeping fingers and eyes crossed).

Dave M.

 

I had this problem on the driver's rear light. I had the dealership take a look at it while getting an oil change a while back. They said it was a faulty light. I don't remember what they actually said because it was about 3 months ago (maybe more). The end result was me paying about $40 to get a new light. I think they just replaced the LEDs. No problems since. I didn't complain about it too much since I had about 50k on the car already.

 

It could be like the problem I had on my Isuzu. Never found the exact cause, but since replacing the lights fixed it I'm sure it was something inside the bulb itself. At first a tap would get it working, then I had to hit it harder and harder, till it finally just stopped working.

 

My first car was a 1967 Mercedes diesel with a taillight problem. It was because the exhaust would enter the light assembly and corrode the connections. It got so I could aways tell a diesel on another Mercedes because the taillight was dimmer on the side where the exhaust was. I ended up making a new ground to fix that problem.

 

Hello all - this is my first post. I have a 2004. Just had my 70,000 mile service and had them look at the rear running light that was out, driver's side. Dealership first quoted $12 for bulb replacement but then looked at it in the shop and they said the entire light assembly on that side had to be replaced ($200). The invoice says, "Necessary to replace lens to get LED strip for taillight. Replaced lens and OK now." They gave us the old part (entire light assembly) and we dissected it. We can find nothing to support their claim for having to replace the entire assembly at $200. There are clearly spots to easily replace 3 bulbs. Weird thing is, we just went out to look at the car; turned on the lights, and the same bulb was out (as before the replacement) on the driver's rear side -- until we tapped on it. Also, one of the front lights was out until we tapped on it. I'm wondering if I spent $200 for nothing-- 1) I did not try tapping on the original before the dealership replaced it, and 2) what the heck are they talking about, this "lens" and "LED strip for taillight"? Anyone have a clue? We could not find such an LED strip in the original part. I could take and post some photos if that would help.

 

The rear light assembly contains six LEDs used for the brake light. If the brake light failed, then the entire assembly must be replaced.

However according to your post, the brake light was not the problem. Rather one of the incandescent bulbs was at fault, which as you noticed, can be easily replaced.

Since the same bulb is intermittent, I suggest you remove it and see if it is new or if the mechanic just swapped the old bulbs from one housing to the other. If the bulb is old, replace it now.

If you still have a problem then there probably is a loose wiring connection, for example perhaps a ground wire that is bolted to the body has a loose connection.

 

Your post is not very clear. There are LED brake lights (that only come on when you press the brake pedal) on top and normal bulbs in the middle (reverse) and bottom of the taillight assembly. If it was the bottom bulb (comes on with the headlights) that is the problem, you paid $200 for a fix that was not needed. You can easily replace the non-LED bulbs by accessing them from the inside of the cargo area.

If you are able to get them to work by tapping, either the bulbs or the wiring is loose. The bulbs could be marginal too and the lighting element inside might just be intermittently connected.

 

Yes I had the same exact problem to the "t" 2008 prius 60,000 miles