2003 LX trailer/towing battery wiring trouble

[Visceral]

Hey all,

I've been searching and googling this all weekend, so if this is in any way obvious, I apologize, but...

I've blown some "fuse" in my 2003 LX470 that supplies +12v to the trailer battery lead on my factory 7-pin towing receptacle.

Background: I have a camping utility trailer that I have a Goal Zero Yeti 1250 in. I've run wires to the Anderson Power-Pole DC input for the Goal Zero Yeti from the trailer junction box so that it can recharge from the truck while I'm driving. The Yeti is capable, however, of drinking 30+ amps.

On a recent camping trip, the 12v+ lead gave up supplying voltage. None of the fuses in the engine bay box appear to be associated (nor are they blown). In the 98-2002 LX series, there was a TSB that spoke of a "hidden" fuse (depending on the year) that would pop if you asked for more than 30 amps. I can't find the fuse, nor can I find one in any of the places that the 98-2002 TSB mentions. The rest of th elighting functions still work, so I don't think I've damaged the little box (wherever it is) that runs the 7-pin trailer connector. It's interesting to me that the little black converter box isn't where it is shown in the 2002 (near the drivers side taillight inside the finder). I havent found it, and the wires go into the loom right under the truck.

I have run +12v to the back of the truck for the fridge, a sub, and a couple other things, and so I might just run a thicker 10ga wire down to the 7-pin trailer receptacle so that 30 amps is no longer going to risk burning the truck down (the wire is not especially thick... 14ga perhaps?... on the stock harness).

But I sure wish I knew where that fuse is.

 

[Mark WV]

first I would double check fuse #5 in the under hood fuse box.

#5 Towing -Trailer Lights
#12 Towing Brake (electric brake controller circuit I Believe)
#16 Towing Tail

I cant locate any other reference to the power lead for the trailer hitch wiring and the ones labeled Brake and Tail are self explanatory, which leaves #5 as the prime suspect. If the fuses are good, then likely the Trailer converter box is no longer feeding power to the 7 pin connector

From another thread- - Member Sandroad posted- "On the '04, the converter is the small orange box inside of the left hand rear quarter trim panel. You can see it by taking off the jack access cover and looking inside to the left, under the tail light. To get full access for replacement, you'll need to remove the rear left hand quarter panel trim."

If the Brake and tail lights are working fine, I agree with your idea of running from your existing 12 V lead to the 7 pin connector (assume that is a fused lead of course) On other vehicles I have typically run a dedicated line from a add on underhood fuse block to the 7 pin connector - no danger of overloading the vehicle wiring with accessories in the trailer- make sure to cut and seal off the wire on the 7 pin harness so you don't feed 12V backwards into the converter box.

 

[Visceral]

Thanks Mark. I've checked all the fuses you've mentioned, and they are all fine and have 12v.

I did notice the little red box, but I was worried that the red indicated some kind of "Dont mess with me! I'm an airbag sensor!!!" or something, and it gets difficult to see all the labels on boxes.

I have an odd feeling that the 12v trailer battery lead doesn''t actually go through the converter box, but I'll check tonight if I get home before it is too dark and family needs take over

I've already ordered the 40a DC breaker, so I'm pretty commited to re-supplying it more safely anyways. Sure isa shame though to have a mystery floating around. Its another reason that I'd love a Factory Service Manual if I could ever find one for less than $200-300.

 

[Mark WV]

I would be interested to know if you do find a fuse or if it goes through the converter box - please post if you figure it out....

 

[Visceral]

I accessed the converter box this weekend (it is the little red box adjacent to the drivers side rear tail-lights). The box was receiving +13 on the "+B" pin... so clearly the open in my system is between the box and the trailer plug OR they are on a different supply. Unfortunately, despite a huge amount of wire "tracing", I was never able to find anything. I actually cant honestly figure out where the wires go without taking the looms apart.

I would really love to consult a factory wiring diagram at this point... there is more to this than is obvious.

 

[Visceral]

I found a reproduction of the factory service manuals on Ebay for $129, so thats on its way now. Hopefully it will solve this mystery.

 

[planomateo]

Sent you a PM.

 

[Visceral]

Thanks @planomateo ! Now to see if my 03' looks like the 04.

 

[Visceral]

I found the answer! After all was said and done, a wiring diagram from an 04 that @planomateo sent me showed me to look at the "30A BATT CHARGE" fuse that is #43 behind the driver side kick panel. Sure enough, it was blown.

I'm really surprised, also in the sense that the blown fuse didn't seem to affect anything else at all over 1000 miles. I've put a new micro-fuse in there and I'll validate tonight that the trailer +B pin now has 12v.

Thanks for all the help, gents.

 

[Mark WV]

Good to know you figured it out. I'm making a note in my owners manuals for that fuse in case I ever run into the issue.

 

[Peludo]

I would like to extend a question that is related to this about the towing charge line on my ‘03 100 series. Feel free to prompt me if I should start a new thread. I thought it would make sense for it to land on the same ears.

I’m on my second off road trailer that uses the charge line and my vehicle response weird anytime it’s in use. When connected and I turn the key off, and even remove it the air conditioner fan continues, the steering wheel permanently readjust up, and next time starting anti-traction and another warning lights(forgot which) come on. I’ve checked the 9 pin trailer connector on the vehicle at the RV shop and everything looks correct. I have also disconnected the charge line on the trailer side (or that 30amp BATT CHARGE fuse you referenced) and it behaves normal. My current solution is to unplug the trailer when I stop for gas etc. and reconnect it prior to starting again. . It’s been a mystery for about 8 years. Did not have this problem on my ‘98 100 the 10 years prior.