2004 Lexus 330 Trailer Harness - No Power

[bicycletroy]

I have a 2004 RX 330. It has the towing package. I found the connector for the trailer lights and connected it but there isn't any power. I have checked the fuses - they are all OK. I pulled out the converter box that the trailer harness connects to behind the drivers side seat. I noticed there were a few diodes there and checked them. They seem OK. Anyone know of anything else that could be the cause? Software upgrade required? Bad converter assembly? I haven't been able to locate a schematic of the converter to see what all it controls and where the input and output from the turn signals is.

[GDixon]

I have a 2004 RX 330. It has the towing package. I found the connector for the trailer lights and connected it but there isn't any power. I have checked the fuses - they are all OK. I pulled out the converter box that the trailer harness connects to behind the drivers side seat. I noticed there were a few diodes there and checked them. They seem OK. Anyone know of anything else that could be the cause? Software upgrade required? Bad converter assembly? I haven't been able to locate a schematic of the converter to see what all it controls and where the input and output from the turn signals is.

There is a main towing fuse that is 30A. Check the manual for the location. Test to see if there is electricity present with a voltmeter. You might even check the fuse with an ohmmeter.

After that, try checking the connections back from the hitch with a 12V test light. The headlights should be enough to verify if the connection works. The turn signals and brakes can be checked later. You'll have to disassemble the rear cargo area if that hasn't been done yet. Instructions at:

http://us.lexusownersclub.com/forums/index...mp;#entry254728

If you have a towing package then an add-on converter is not necessary. Just plug the wire that came with the hitch into the harness. A *.pdf file in the above post has the location if you didn't do the original wiring yourself.

From you post, it appears you are well-acquainted with electrical testing procedures so check every connection from the hitch to the fuse until you find power. After getting past the converter use the voltmeter instead of the 12V test light.

[code58]

I have a 2004 RX 330. It has the towing package. I found the connector for the trailer lights and connected it but there isn't any power. I have checked the fuses - they are all OK. I pulled out the converter box that the trailer harness connects to behind the drivers side seat. I noticed there were a few diodes there and checked them. They seem OK. Anyone know of anything else that could be the cause? Software upgrade required? Bad converter assembly? I haven't been able to locate a schematic of the converter to see what all it controls and where the input and output from the turn signals is.

I believe most factory tow package equipped vehicles use a relay in the fuse box that is normally supplied (but in the glove box along with a plug and pig tail). I'm not sure about a Lexus but the package is normally in the car somewhere when delivered new. Did you buy the car new? Most people don't know what that package is for even and it soon gets lost. They don't install the relay because then that outlet is hot and a lot of people never use the vehicle to tow, hence no reason to have the plug outlet hot.

[bicycletroy]

I did a continuity check on the fuse but didn't do avoltage test. Can I check the voltage by turning on the lights and putting a VOM across the fuse? or do I need to pull out the fuse? IWIll the headlights provide a voltage across the fuse?

Thanks for the help

[GDixon]

I did a continuity check on the fuse but didn't do avoltage test. Can I check the voltage by turning on the lights and putting a VOM across the fuse? or do I need to pull out the fuse? IWIll the headlights provide a voltage across the fuse?

Thanks for the help

If the 30A fuse tests OK with an ohmmeter and there is power to the fuse (lights on) then it is time to check the the wiring harness pigtail by the driver's side rear wheel which is under the cargo area for 12 volts (lights on). In essence, you are tracing the electricity, or lack of it, back from the hitch to the fuse to find out where the breakdown has occurred. Keep going backward from the hitch, checking every connection, until heat is found.

You could pull the 30A fuse and check for power to one of the fuse leg sockets. If the fuse tests OK with an ohmmeter and there is power to one fuse leg then the issue lies elsewhere. If you'd rather test each connection forward from the fuse to the hitch that is an option as well. The color of the wires can be your guide.

There is a post somewhere on this site with a wiring diagram for an RX300. The trailer wiring should be the same for a 330 and a 350. (Ah - here it is

http://us.lexusownersclub.com/forums/index...ic=8347&hl= )

It is rare for the problem to be a bad wire but not out of the question. Finding such a thing is a pain in the rear but keep at it and it will show up eventually.

[bicycletroy]

THank you - I will pull the fuse and look for voltage. I already tested for voltage at the pig tail and got nothing. The pig tail plugs into a converter box - I'll try there also. I'll post what I find in the event someone else has a similar problem.

Thanks for the wiring diagram link. I requested those the other day also. Nothing yet. I see I can buy the wiring diagram on E-bay if necessary.

[code58]

THank you - I will pull the fuse and look for voltage. I already tested for voltage at the pig tail and got nothing. The pig tail plugs into a converter box - I'll try there also. I'll post what I find in the event someone else has a similar problem.

Thanks for the wiring diagram link. I requested those the other day also. Nothing yet. I see I can buy the wiring diagram on E-bay if necessary.

Could be wrong but I believe that link has been dead for a few years now. It is from '04 and from what I remember the guy refreshed it once but after that- nothing. I know a lot of people have requested wiring diagrams over the years but maybe someone could post if they have had luck with that link since early on when it was posted in '04.

[bicycletroy]

I turned on the head lamps and put a volt meter across the fuse. No power. Where do I check next? missing relay? No reply from the person that was offering up wiring diagrams. I did buy a Haynes manual. It has wiring diagrams but not one that has the optional towing package.

[kulikuli]

Any luck with your problem?

I have the same issue with mine and haven't work it out yet.