FastEC

I purchased my 2002 RX300 new with the towing hitch and 4-pin electrical connection already installed. I had never had a need to tow anything with my RX for all these years but recently purchased a 5x8 enclosed cargo trailer. My brake lights and turn signals work fine on the trailer but the running lights will not work when connected to my RX. I tested the trailer with my neighbor's Ford F150 and everything on the trailer works fine. So, I tested the 4-pin connecter on my RX with a 12 volt tester and the left and right signal connections lit up the tester fine but I could not get any power to the running light connector (brown wire). I looked to see if a fuse was blown and found that, even though I purchased the towing package, the fuse slot labeled towing (slot #2) was empty. I purchased 20 amp blade fuses and tried 2 new fuses, but it still didn't work with either fuse. I just took it to Truck and Trailer USA today and they could not get any power on the running lights either and suggested I take it to my Lexus dealer. I called my mechanic and he thinks that the computer may need to be programmed to allow the running lights to work. I called and set up an appointment with my Lexus dealership, but they had no idea when I asked if it needed programmed to turn on the running lights (this is the world's largest Lexus dealer by the way). My mechanic says that he sees this happen when installing fog lights, etc. on cars that never had them before, that they won't work until you tell the computer to allow them to turn on. Does anyone know if this is the case with why I can't get the running lights to work? Any help would be appreciated.

salimshah

Things may have changed from year to year. '99 model, I had to tap into the tail lights and run wires to an electronic module. +12v, gnd, Lturn, Rtun, Lights & Brake. The module went bad after 8 years and to test it out, all I needed to do was to check all the inputs for supply voltage . The turn signals would go to 12v and zero as evident that the module based on the blink. Once inputs test out good, and the outputs do not behave properly, the diagnosis is the module is bad.

You can do the same test.

The module takes the turn signal and uses it to make and break the brake lights.

Salim

Possible correction:
I think there is no +12v connection.

sktn77a

iTrader: (2)

Could be a bad connector/cable but the early OEM RX towing package light modules were notoriously unreliable. This was supposedly improved by 2002 but the basic design was weak.

Expensive to replace but the OEM module doesn't require cutting into the car's wiring harness like most of the aftermarket systems do. You don't need to reprogram anything - I think your (Lexus) dealer was correct.

386Lexus

I had this same problem and solved it yesterday. It turns out that if your towing package was installed by the dealer it is very likely that when you go to look for the Towing Fuse in the main engine compartment fuse box you will find it missing. I suspect this is because of the difficulty of wiring all the way back to the fuse box post-manufacturing.

I used a simple electrical tester to determine that power was not coming out of my 4-pin connector below the bumper for the tail light (brown wire) pin. Power was coming to the green and yellow turn signal pins. So I knew the problem was not with the trailer but with the electrical in the SUV.

I then went under the car to begin tracing back the wires and had the same problem all the way back to where the group of wires turned up into the body of the SUV. I then pulled open the back and lifted the spare tire out and removed the side cover and the basket it covered (just pop the plastic rivets off and unscrew the base screw). I then found where the wires had entered from below.

Along the wires I found a small plastic fuse holder with clip that was labeled "tail light". Mine was white. I opened up the clip and, sure enough, there was a 5 amp fuse inside and it was bad. I replaced the fuse, hooked up the trailer harness and the tail and running lights worked fine.

Hope that helps the next person with this problem.

biff44

gosh, i have the same problem, but with a 2007 RX350 with the factory installed tow package. the brakes and directionals work fine, but the running lights do not turn on.

i will look for a fuse...i have the back interior all removed. but i do not remember seeing one!

i just spent about an hour trying to figure out where the wires go to between that 30 Amp fuse in the enginer compartment fuse box, and the wiring bundle in the back of the car. there has to be a controller module somewhere, but for the life of me i can not figure out where it is, or even a part number to order for it. i see PLENTY of trailer tow relay controllers for 2010 and up....but nothing for my 2007 generation.