I've searched and I saw at least three other occurences of thsi problem, but I haven't seen a solution. Does anybody know what causes this?

I have a 99 RX300 and was towing a trailer (factory installed tow package) when the driving lights went out. The brake lights work, the license plate works, but the driving lights in the back are out (front lights work). Both bulbs are fine and I noticed that there is no power going to the rear tail light section other than the brake light and turn signals. Driving light power is not coming through. No warnings on the dash either.

Any thoughts?

 

Do you have the required "isolating module" to make connections to the trailer hitch. [You should not simply tap in to the existing wires, to power trailer lamps].

Start by checking the fuses.

I hope it is as simple as that .

Salim

 

Yep, all fuses are good (I actually pulled each one in all three boxes to verify). The rear license plate light is supposed to be on the same fuse and it works, so that also makes me think it isn't a fuse issue.

There is a module from the factory near the spare tire that converts the 6 wire tail light harness to a 4 wire trailer connection, but i've lost power from the driving light harness prior to that connection. I'm wondering if the driving light switch on the steering column can go bad and kill the driving lights in the back only?

 

If you apply the same logic ... since the lic plate light works then the switch (stalk on the driver pod) is working too. I am

Salim

 

Good point. Hmmm. Well, i've got an appointment for them to look at it tomorrow. I'll report back with what they find.

 

So, apparently the dealer says that the "smart box" has gone out. No idea what it is, but apparently its located in the trunk area and is integral to the trailer hitch assembly. The cost is around $500 ($300 for the part and $200 for labor).

I hope this is different from the trailer harness 6wire to 4 wire converter that comes with the factory tow package, because that thing is a $20 part. I'll know more when its done next week.

 

"smart box" is the isolating module.

If you are willing and able you can do the work too.

Here is my knowledge about the "smart box" and wiring. For various models the wiring may be different.

Note: I have a '99 RX and I added the module when I installed the hitch.

The module has a power and ground line. I had to connect the power line to +12v accessory plug in the rear hatch area and used a screw to connect the ground. Then it has two umbilicals each goes to the bulb sockets on each pillar on the back to connect to turn signals, brake lights and night_rear_lights. Wiring is such that you plug in the umbilical to the wire and the umbilical has a new plug for the light bulb [I don't remember if it taps of voltage {parallel** or the rear bulbs are provided juice from the module(series).]. The third leg of the module goes to the connector for the trailer.

If you have the same setup, you can open up the rear of the lights and bypass the module or check voltages at the connector. That can save you the labor charge of $100/hr (est)

Salim

 

In case anyone ends up having to do this themselves, the part number is:

Toyota: 89373-20240
under that is another number: 271000-0540
The module has the words "Lamp Failure" cast into the housing which seems ironic.

Total cost from the dealer was $538 out the door. The cost of the module was $289.23 by itself.

 

My dealer lists it for 403.26$ my cost 278.11$.

 

FYI - Blew out my second module last weekend.

$300 ordered online.

Seems that if I leave the light on inside the trailer, the extra current draw from the trailer light (tiny little bulb) is enough to overload the module and burn it out.

If you tow a big trailer (6x10 in my case), be careful with interior lighting.