Wiring Harness For Trailer

[tealboy]

any tips on wiring the rx 300 so i can connect trailer lights? the dealer wants a fortune to do it and said a special modulator is also needed due to computer complications.

cant you simply run a hot wire from the battery to the modulator and then the wiring harness?

what is the modulator and how expensive are they? anyone done this?

[RX in NC]

I should caution you to carefully study the many threads on this forum pertaining to early transmission failure in the RX300 series before you make a final decision on whether to use your RX300 as a tow vehicle, especially if it is all-wheel-drive. Based upon what we've been through with ours, I would never tow anything with it.

[dgorrie]

Might be worth checking with U-Haul and seeing what thgey think. They get a lot of practice an installing tow hitches.

[jvmitche]

Well, I'd hesitate to make blanket assumptions about everyone's towing. I have a 500lb 17ft sailboat that puts very little stress on my '99 AWD RX. However, that's not to say there's no towing issues AT ALL with the RX. I tow a 18ft Bayliner Runabout a few times a year, but do so very gingerly. I know very well that my transmission is a delicate flower, so I try to excessively careful when towing AND when NOT towing.

As far as the wiring harness issue goes for the RX, I lived this one and will help summarize here. The posts on this board are helpful, but very scattered and sometimes innacurate about this particular issue.

The RX either came with the towing package or not. If you have the towing package, you can just buy a little wiring harness that attaches underneath the vehicle. If you do not have that towing package, you'll have to purchase the brainbox/lighting controller AND wiring harness.

1) How to tell if you have the towing package? Get underneath the car and look for a rounded plastic cover that sits near the driver-side rear wheel and straight down from about where the fuel door is. Underneath that plastic cover you'll see a bunch of wires all wrapped up very tighty and a rubber gasket -- this is the entry/exit point into the vehicle for wires. If you see a square white plug (ie: something you could plug a wiring harness into) dangling underneath that plastic cover someplace... CONGRATULATIONS, you have the towing package. That means you can buy the $20 harness hook it to that white plug and start towing. If not, sorry, you're going to have buy the toyota brainbox/controller and install it.

2) If you know for certain you need the brainbox, call your local Lexus dealer and ask for the Wiring Harness and Controller for your particular model year RX. I know when I called they mentioned they've switched some of the part numbers around recently, so rather than give you inaccurate information, I'll just recommend you do what I did. Once you have that information, you can go online or call around. I think the Lexus dealer quoted me $180 or so for the part -- I ended up paying about $140 from www.lexuspartsmall.com in Milwaukee. I was originally concerned about installing the part myself, but once it arrived and I saw the very detailed installation manual I knew I was OK. Quick summary, the brainbox mounts in the trunk below the spare tire, taps into the large cluster/trunk of wiring that comes from the front of the vehicle, then also taps into each side of the rear lights. It sounds worse than it really is -- there is no cutting/splicing or anything like that -- it's all pretty simple. Taking apart some of the interior panels to access the wiring can be a bit tricky, but the manual included with the part covered the order and how to remove everything. From the newly mounted brainbox, the wire with the white plug goes down through that rubber gasket and sits underneath that plastic cover. From there you take the wiring harness and plug it into that white socket and then mount the connector on the hitch. I had a non-standard hitch, so I had to drill and tap a couple holes....but it worked great.

One note -- I know there are non-OEM parts that get this same result, but I was a little scared. There is a ton of electrical systems in all these newer vehicles and splicing wires and tampering with the system has led to some horror stories. This way of doing it prevents the rest of your electrical system from being damaged if something shorts or goes wrong with your trailer wiring.

All in all, it took about 2-3 hours. But I have a feeling the dealer would have charged at least 1.5 hours labor. It was worth it to me, plus I feel like I learned something I can use in the future for working on my RX.

[jvmitche]

I did some searching through my emails, the exact part number for a 1999 Lexus RX300 Lexus/Toyota Trailer Wiring Harness/Controller is:

0892148051

I also see earlier this year I got a price quote of $109 from www.lexus-parts.com. Hope this helps!

[tealboy]

Thx JvMitch,

I looked and i have the wire coming down, though it seems to go into a rectangular plastic box that is seemingly attached to the bottom of the gas tank. I also looked at the orig invoice and it said "tow pkg", so i know i have it.

Where is the end that i need to tap into with my pigtail? Is in the plastic box?

[tealboy]

RX in NC, not to worry, it is a small boat (grady white). I'm pretty sure it doesn't weigh over 5000 lbs, lol. Actually, just a small jon boat, though i will also use the vehicle for off road use, lightly, which is why i wanted awd in florida.

[jvmitche]

Hi Tealboy,

That rectangular plastic box is the plastic cover I was referring to. You'll have to remove that box to get to that white tow connector/socket. If I recall I just used a ratchet with the appropriate size socket -- it came off very easily and simply (just don't lose the screws!) You're right though, it's right next to the gas tank and filler line.

Once you get that cover off, you should see a square/rectangular like socket with (I believe) 4 holes in it -- of course it might be covered with a gasket or something to keep the weather out. That is the connector that runs to the controller and brainbox inside the vehicle. You attach the wiring harness (ie: the thing that mounts to the hitch itself, the thing you plug the trailer into) to that white/square plug. Then just route the harness toward the hitch, use some zip-ties to keep it all secure. The Lexus/Toyota factory hitch has premade holes for mounting it to the hitch. I have a non-standard hitch, so I drilled two holed and tapped them. It looks and works great!

Let me know if you need some pics, I could take a few this evening/tomorrow and show you what I'm talking about. I'm very passionate about this because I spent so much time trying to get the wiring system installed. I also know how many people use the search function on these forums -- hopefully someone will benefit from this again in the future. Not to mention, I've taken a lot of info from this site -- it's time to give back.

[tealboy]

i think all of that is very clear. i will crack the box tomorrow and take a peak. I am lucky i suppose. even the hitch, which i ordered from ebay is awesome. it is a curtis, made specifically for the rx 300 but was being cleared as old inventory. i paid $81 for it, plus 23 to ship. It went right on and looks terrific. now the wiring, which will now be easy.

thx for the tips.

[Magnoman]

I have a 2002 rx300. went crazy with this a few months ago. I was told by one dealer you need to take off half of the rear cargo panels on the drives side find a conncetor. I did this found a connector that was not the right one.

The bad news you need the little wire harness kit from Lexus $200.00. Comes with a blue relay switch with you do not need, and a wire harness. after getting the kit & wire harness no one at the dealer could tell me where this connector plugs in. They sent me to another dealer who installs hitchs

and said they could tell me? So after driving all day went to the third dealer and begged them to

have someone show me where the connector is for the wire harness! presto!

right under the back of the car there is a black plastic box. remove the four 10mm bolts take off the

box there it is! the connector!!!! just plugin the wire harness, put the cover back on.

One more thing! there is a fuse that has to be put in under the hood fuse box, there is a empty

spot that says trailer lights.! Your done takes about 15mins. after days of calling and running

around!

[tealboy]

thx for the comments on the wiring for the rx. the fuse would have gotten me for sure. regarding the black box under the rear w/ 10mm bolts. i took that cover off and found a square, grey socket that has 4 prongs. Is that what i plug into? It is an unusal prong type, so where do i find the connection? the pigtail that my trailer hooks to is std, but the square four prong under the veh is unique.

thx

[jvmitche]

You got it. That grey socket is the wiring harness connector. I assumed

you had the part before, but you may need to buy it still. It's

basically a harness of wires that on one end has the grey socket

connector, and on the other end has a female standard trailer wiring

connector. So, once installed, you have a grey socket, a connector into

the grey socket, and a wire running back toward the actual hitch. THEN

you attach your trailer wiring to that wiring harness female connector.

If you have a standard Lexus hitch, there will be two mounting/threaded

holes on the hitch itself. Those two holes allow you to attach the

wiring harness bracket that comes with the oem wiring harness to the

hitch to complete the install. My point was I have a non-standard hitch,

so I had to drill to holes and use a tap-and-die set to thread the holes

and mount my bracket.

Here are a couple pics, I think it will help illustrate it. You'll note

my grey connector doesn't really make it all the way under the plastic

cover. That's because I had to route it there myself from the inside of

the vehicle (when I installed the controller box), through that rubber

gasket. Looks to me like I'll need to re-wrap some of my cables with

some better adhesive tape -- the black electrical tape isn't cutting it!

[mikey00]

Just a word of caution on the wiring info. I had a 2000 RX. Back then the towing prep package was an option and if you didn't have it a wiring kit was required that connected to individual lighting wires by removing panels in the back cargo area. It was a fairly complex install. When I got my 2001 the towing prep package was standard. That means you have the transmission cooler and the wiring plug in the plastic compartment under the car as discussed above. This plug is already attached to the individual lighting wire through the wiring harness which makes things a little easier. The info presented above leads you to believe that you just need to plug the harness into the plug add the fuse and you are good to go. Not so. You are also missing the controller/brain. Still, the controller/brain is just another simple plug in install. A search on this subject should provide you with all the necessary part numbers as it has been discussed a lot in the past.

[tealboy]

Now I am really confused. I thought by having the tow package and the plug discussed above, all i needed to do was connect my wiring harness and add a fuse, but mikey, you are suggesting otherwise.

the tow package does not include the controller/brain necessary to run the lights? where do i get it, how is it installed and how much does this item cost?

[mikey00]

Now I am really confused.  I thought by having the tow package and the plug discussed above, all i needed to do was connect my wiring harness and add a fuse, but mikey, you are suggesting otherwise. 

the tow package does not include the controller/brain necessary to run the lights?  where do i get it, how is it installed and how much does this item cost?

←

Check this link.

http://www.clublexus.com/forums/showthread...ng+prep+package

[jvmitche]

Well, I think some of this might have to do with what particular year RX we're talking about. Mine was a 1999 and I definitely DID NOT have the Lexus tow package, so it was a simple matter. I guess I would do two things. You could call the Lexus dealer and give them the specs on your vehicle and ask them what you need. I'm fairly certain you do NOT need the brainbox/controller, otherwise what is the point of the towing package if you can't tow without adding a $200 item? Also, open up your trunk, lift the rear floor, take the spare tire out, and take out those plastic storage bins that are under the floor. Then see if you can trace the cord that eventually terminates in the grey connector. It might lead you to the controller box itself.

Here are a couple of pics of the lighting controller.

Mikey, I'm not sure quite what you're saying -- since I found pretty much the opposite when I did all my research. I think the different model years combined with the fact that many people put not factory hitches on their cars makes it confusing. I will say this, if you have a grey connector underneath that plastic cover, and it gets voltage with a voltimeter when you use the rear lights, you definitely DO NOT need the controller.

[lenore]

Well, I think some of this might have to do with what particular year RX we're talking about. Mine was a 1999 and I definitely DID NOT have the Lexus tow package, so it was a simple matter. I guess I would do two things. You could call the Lexus dealer and give them the specs on your vehicle and ask them what you need. I'm fairly certain you do NOT need the brainbox/controller, otherwise what is the point of the towing package if you can't tow without adding a $200 item? Also, open up your trunk, lift the rear floor, take the spare tire out, and take out those plastic storage bins that are under the floor. Then see if you can trace the cord that eventually terminates in the grey connector. It might lead you to the controller box itself.

Here are a couple of pics of the lighting controller.

Mikey, I'm not sure quite what you're saying -- since I found pretty much the opposite when I did all my research. I think the different model years combined with the fact that many people put not factory hitches on their cars makes it confusing. I will say this, if you have a grey connector underneath that plastic cover, and it gets voltage with a voltimeter when you use the rear lights, you definitely DO NOT need the controller.

←

I have a 99 RX300 and the little controler box is a converter from the asian/european wiring to american trailer lights. Mine died and I went to Walmart and replaced the Lexus controller with a generic off the shelf one. works fine and cost only $12 . It has to do with the seperate brake/running lights conversion.

[mikey00]

I think you are right with the statement about different years causing the confusion.

tealboy: You never said what year you have, so I am not sure what is the correct answer for you. I can guarantee you that a 2001 with the towing prep package did not come with the controller/brain. It was called the towing prep package and consisted of the trans cooler and the plug in the compartment under the car. The point being that if you wanted to tow the controller and pigtail is just an easy plug in and the hitch a simple bolt on once you have the towing prep package.

Here is one of my old posts from a competing site:

"Here is everything I know about the RX300 tow hitch wiring and all the confusion that surrounds it. Pre 2001 RX did not have the hitch wiring built into the factory wiring harness and required a more complicated kit with connectors connecting to individual taillights etc. It required more labor to install it. Everything following pertains to the 2001+ RX. If you buy the hitch package from Lexus you get hitch, pigtail wiring connector, 20 amp fuse and control module (Lexus part#08921-4870).

I purchased a pigtail from ToyotaGuys.com ($12) for a 2001 Highlander complete with the fuse and directions (Toyota Part#00016-48102) as did many others and we found after installation the trailer lights would not work. I have since went to the Toyota Guys website and the part is no longer there. Anyway, it was determined we needed the Lexus control module 08921-4870 which is about $80 from the dealer. Once this is plugged in everything works. It mounts on 2 studs in the cargo area near the spare and plugs into a connector there. Not to confused with the pigtail connector, which plugs in underneath the car.

If you want the pigtail it can be had at etrailer.com for $13. They have directions on the site complete with pictures of it and where it plugs in under the car. The pictures are actually a Highlander but the RX is the same in this area.

My opinion: The neatest install is had by buying the plug in parts and plugging them to your wiring harness, which is already wired for the tow hitch. The quickest and easiest install is to stop at a trailer place and have them do it. They usually do it by tapping into the taillight wires as done on a pre 2001 but the cost will be about the same because they don't need the $80 module.

Mike "