knocker

I borrowed this from another site to use as a reference.
This is the easiest and cheapest way to add wiring to
a RX300 without the tow package pre installed.
Worked for me. Good Luck!

First let me say I have my degree in electronics and own my own company installing phone systems. I have installed hitches on my Saab's - so I am familiar with the process. But overall it's a pretty easy job for anyone with basic tools and skills. The wiring parts I used are the same parts local tow shops use.

I have a 2002 FWD RX300 with NO tow prep package listed on the original window sticker. After looking, I did have the tow wiring connector (where the factory brain/controller would plug in) by the spare tire and also the pigtail connector under the car in the box under the spare tire.

I purchased a very nice quality and good looking hitch from eTrailer.com - installation was very easy - took about 30 minutes total. (#70777) This hitch has the tube contruction which I think looks better than the square tube ones the local people carry.

I purchased a DrawTite ModuLite trailer light power module (#118146) and a Hoppy Mag Flat Bracket kit (#48085) both locally. The ModuLite you have to have. The Hoppy part is just the wiring and 4 wire connector that goes down to the trailer. It is nice because it is already wrapped and has a magnetic housing that keeps the connector out of the way. But you can use any 4 wire connector about 60" long.

Here is a rundown of what I found out about the wiring. As stated above, my car did not list the tow prep package but did have the connector by the spare tire (a white 10 pin - 9 wire- female rectagular brain/controller connector) and the 4 pin -4 wire- grey housing pigtail connector in the rectagular black box under the car under the spare tire, I did not use this connecter. This 4 pin connector is wired up to the 10 pin connector.

I tested the pins on the 10 pin connector (without the tow fuse in the fuse box under the hood) to find out which pin controlled what. Here is the breakdown-

Looking at the connector with the snap pin up. Looking at the connector the pins are shaped like a U. ::..::

The left side red 4 wires come from the pigtail under the car, these are not used in my installation. The 3rd pin over from the left on the bottom has no wire connected. The 4th wire over on the bottom is the Power that is hot when you put in the tow fuse (don't put the fuse in now). the 5th pin over from the left on the bottom is the Brake light, the 6th pin over from the left on the bottom is the Right turn signal - this is the last pin on the bottom row. Right above the right turn pin is the Left turn pin, this is the top row most right pin. To the left of that is the Running light pin.

The instructions with the ModuLite are very short. The RX uses the 3 wire system. The only thing different and a big disclaimer --- the instructions state to connect the black battery wire directly to the battery --- I chose to use the power on the connnector coming from the fuse box. You can make up your own mind on what you think is best. I figured this is how the factory brain would power the lights so I chose to use it. I did not feel like snaking a wire up to the battery.

Remove the spare tire. Follow the short ModuLite directions. The kit includes wire taps but you will need additional taps - both blue ones and a yellow 12 guage wire tap if you chose to use the connector power. Splice the ModuLite wires into the correct connector wires behind the 10 pin connecter using blue taps. . The black wire (if you choose) splices into the power wire using the 12 guage tap. Stagger the taps so the bundle does not get too big. I connected my ground wire to a bolt right on the ridge below the hinge of the spare tire cover. The Modulite unit comes with the trailer 4 wires and connector on it, but you would have to cut a big hole in the grommet to get through the body, so that's why I bought the seperate Hoppy tail/connector so I could just cut a slit in the grommet and feed the wires up through. Makes a nice tight seal. Splice the Hoppy wires onto the same color wires on the Modulite trailer side.

I had a little 3 dollar tester that plugs into the trailer connecter to test the installation. Put a 20 amp fuse in the spot labeled Tow in the fuse box under the hood. Plug the tester into the trailer connnector. Test the running, turn and brake lights. I taped and tie wrapped my wires and mounted the modulite with some double sided tape to secure everything.

Well I hope this helps someone as I was very confused on how to get this going. I thought I would have to buy the brain/controller from lexus, but this is how the local tow shops do it. Seems to work great and I saved alot of money! I have a picture that I hope gets attached. If not let me know I can send it to you.

sktn77a

iTrader: (2)

My first towing package "brain" fried after the second use (99 RX300). I replaced it with the revised module (apparently I wasn't the only one who'd had this problem). Lots of interior panel removal to do this - took me half a day. This is about the same as it would be to add a factory module to a car without the tow package (I believe they all came pre-wired to the spare well). I looked at the e-trailer units, but at that time (2 years ago) their instructions had you cutting into the factory harness at the rear light.

Thanks for the info!

Hatchman

Great info! I'll be doing this soon. Anyone have any pics of this install?

hypervish

I remember seeing a video of an installation for the trailer wiring harness on youtube made from etrailers.. Let me see if i can find it. http://www.youtube.com/watch?v=tAJa6FQWpE0

sktn77a

iTrader: (2)

Yep, that's the one I saw also. Didn't like the idea of splicing into the cars wiring harnesses behind the rear lights or the additional splices he had to do because the etrailer harness as supplied was too short for the RX300.

Hatchman

Thanks for the great write up and excellent info! It appears that some of the 2001 to 2003 RX300s came with the "brain" from the factory if equipped with a tow prep package, and all that is needed is this part from etrailer:

Trailer Wiring Harness - 2001-2003 Lexus RX300
for Lexus RX300 with Factory Tow Package


Part: 118245

I installed this wiring harness to the four prong connector under the car in the black plastic box and plugged in the supplied fuse in the "tow" slot and everything worked! Installed the Hidden Hitch (#70777) and install was super easy. Interesting that the Hidden Hitch tube type was rated at a 4 out of 10 for difficulty and the rest of the hitches are only a 3 out of ten. Could be because the 5000# rating is higher and perhaps this hitch is a tad heavier. Looks great and all the lights work perfectly!

Thanks again for all your inputs!

MattyP12

Hi,

I have an rx300 2003 and installed the same trailer wiring harness but cannot get power to lights? I inserted the 20amp towing fuse under the hood. What am i doing wrong? Do I need to activate something?

Best,
Matt

speedy6

iTrader: (6)

You vehicle might not have the tow package kit, that is why it it not working. I too also purchased this plug and it does not work as well. We might have the plugs, but the lines might of not been placed. Most AWD RX300 had the tow package lines standard.

Jordan

Lynsygirl03

Do you still have the picture you referred to by any chance? I bought the trailer wiring harness that plugs in underneath the car, but my car is the 'O2 RX300 with FWD so it didn't previously have the tow package setup. It sounds like your solution is what I'll need to do but any visual help would be useful. Thanks in advance if you can help.