towing electrical problems

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“he had done 2 landcruisers year unknown but he said they were using his memory 2001 and 2003, after working on them he advised the owners to just put in a new harness”

Does the newer Toyotas have a 7 way wiring harness? Or is it just the standard 4 way flat?

“remove pos battery terminal from trailer battery everything ok--power is therefore coming back from the trailer, trailer schematic shows the pos and ground leave the trailer side and return to battery on trailer.”

Exactly, whenever the power is disconnected the problem goes away. So a diode or battery isolator should do the trick. The isolator will cost more but you can experiment with a diode, the diode will be the least expensive to experiment with. If it works then you can go either way isolator or size a proper diode. You will need to size the diode so start with radio shack pn# 276-1661.

Tell me how your positive wire is run to the trailer. Is it directly to the battery with a fuse? (If it’s going to the fuse block, than that could be part of the problem. Make sure your ground is good too.)
Make a simple jumper lead between the battery (either end) and test for your problem. This can be hooked up anywhere between the two batteries making sure the direction is going to the trailer. The easiest place would be the battery + terminal on the trailer.
 
electrical problem

thanks Dean i will try and do that this weekend, but i may not be able to get the diode til monday, i was going to look at the optima yellow for my trailer anyway

david
 
electrical problem

Hi Dean i had some time and decided to do some checking here is what i found, if i start up the lexus then plug in the trailer, then turn of the lexus the dash lights will remain on and the rear wiper will run but only for about 1min, the instrument panel lights remain lit and will not go out, if i disconnect the ltrailer the lights will go out, if i theni connect the trailer with the engine off all is well even though there is a constant 12.75 volt at the at the plug, checked with a digital multimeter,i dont know if all travel trailers have this constant voltage.

david
 
All trailers with a 7 way plug will have a constant 12v.
I thinking there is a problem with the factory 7 way harness on you 100. My thought is the 12 battery wire is connected in you fuse block. And it’s the stray voltage back feeding whenever the engine is turned off causing your problems.
I would trace down the 12 constant wire in you fuse block. Then remove the fuse to kill the circuit.
Then try your problem one more time. If the problem doesn’t happen, then try this.
With the fuse pulled from the 12 volt wire, disconnect the trailers 12v wire on the 7way plug or you trailers battery which ever is easier. (The wire should be black, but check to make sure it’s going to your trailers battery +).
Now take a length of wire connected to your cars battery and connect it to your trailers 12v wire. (This will eliminate the fuse block in you 100) Now check one last time to make sure you don’t have any problems.
If this works, then you will need to…
A) By pass the fuse block and wire it directly to the battery.
B) Install a relay to turn it off when the key is off.
C) Keep the fuse out. This will result in your trailer battery not being charged while connect to you car.
Hope this helps.
Keep us posted.
Dean
 
electrical problems

thanks Dean it goes into lexus friday morning i will print out your advice and take it in with me, i will keep you informed

david
 
10-4
Dean
 
electrical problem

well i picked it up from lexus, they checked everything and found it ok, i could not take the trailer with the car, i did talk to the auto-electrician he said i should make sure that the two harneses are in sinc, he said i should use a battery to check both. if all is well here - it was checked - but he said i should double check then i should have the hot wire from the cat re-done, just as you said, he said contacting lexus in his opinion be fruitless as these are made in japan and noboddy pulls trailers there, so i will do what as been adviced - at the moment its cold here and raining,so i will have to wait.

thanks again Dean
david
 
Just ran into the same problem with my 03 LC. The dealer spent three days working on this problem and got no relief from Toyota. What's particularly annoying is that they didn't just fess up and admit there was a problem. Instead they wasted the engineer's time, and mine. At any rate, I like the diode idea, I just wasn't clear on where it goes. A previous post said (I think) the black wire, but is this on the trailer or truck side? I'd kind of prefer to work on the trailer side -- the position of the wiring on the truck is hidden under the dash and nobody (dealer or rv guy) wants to make any change to the truck because of liability. I'd be willing to do this if I could actually reach it ;)

Thanks, Scott
 
PS The Toyota engineer gave me the wiring diagrams for the hitch electronics. Also the next year's electronics, where you can see they installed in extra relay. Doh! If anybody is interested, I'll post them.
 
please do
 
Here are the schematics. My 2003 LC has 2004 wiring, which I've heard is not unusual. Notice the B24 junction on the 2004 schematic which got changed out to fused connection to power in 2005. The Toyota head tech who worked on my car believed this was added to address this specific problem. I don't know whether this change alone would fix the problem. The tech at my local RV shop suggested putting a power disconnect switch on the trailer battery because he didn't want to touch the truck.
 

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thanks. will check the 03 sometime to see if that relay is new for 04
 
Cool. Can you tell from the schematic which wire you installed the relay on? I've ordered some 15V 20A diodes and am thinking this should go on the black "2" wire.
 
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