LMM Factory Towing package wiring

[Dean E]

Gents, just got back from our spring bike trip. Went down to the southern part of Texas to ride the hill country there. Had a great time. Before leaving I went thru my 7x12 enclosed trailer. Redid the suspension since it was getting pretty loose. Everything including the electric brakes worked perfectly. We started back to Nebraska Saturday since the weather turned rainy and cold. We were bucking a serious headwind most of the trip along with the rain. That evening as we approached Oklahoma City it got dark enough for the auto lights to come on. After a few minutes I noticed my trailer running LEDs were not on. Pulled over and found my #22 fuse up in the engine bay labeled TRLR PRK (15 amp) blown. Put a spare in and within about 4 seconds it also blew. Had to call it a night once it got too dark.
Got back home today and got into the light issue. Turns out it is not my trailer causing the problem. The fuse blows with nothing connected trailer wise. Here is what really baffles me. With the blow fuse installed and the running lights turned on I can see 12 VDC on the power leg of the fuse. I switch to continuity on the fused side and look for resistance to ground off of the battery and it is open. I have been troubleshooting aircraft electrical systems for over 30 years but the factory wiring prints for autos and trucks has been far from ideal especially when a factory option is installed. Does this lighting circuit go thru some module that I am not aware of? I have some wiring prints but nothing for the trailer option. Any prints or insight on this would be much appreciated. Thanks, Dean

PS. Bucking that head wind through most of Texas and Oklahoma pulling the enclosed trailer dropped my mileage down to about 8mpg. Man I was very thankful I installed the S&B 62 gallon tank on my truck!

 

[NC-smokinlmm]

I believe it goes thru a module that is also associated with tire pressure monitors if I remember correctly. I think it’s above the spare tire.

 

[2004LB7]

Doesn't look like the circuit goes through any module. Just straight from the fuse, to the X414 connector, then to the trailer connector

 

[NC-smokinlmm]

I was thinking about the Tpms module that shares duty with the remote door receiver. I did have to change out the module or whatever it is near the spare tire.

 

[1FastBrick]

So that's a brown wire. It goes back to Pin F on the trailer connector at the bumper. Attached is the wiring from that fuse to connector.

However it is also spliced into a fifth wheel harness and those wires can be bare under the bed. They are usually taped up under the bed near the Fill port area. Maybe its touching ground and causing the short. That is assuming you don't already have it wired into a plug. Also check the plug that goes into the back of the port on the rear bumper. Corrosion can get in there and cause a short as well. Last but not least, I have heard of a few cases where that plug housing assembly it self has an internal short and has to be replaced.

 

[Dean E]

So that's a brown wire. It goes back to Pin F on the trailer connector at the bumper. Attached is the wiring from that fuse to connector.

However it is also spliced into a fifth wheel harness and those wires can be bare under the bed. They are usually taped up under the bed near the Fill port area. Maybe its touching ground and causing the short. That is assuming you don't already have it wired into a plug. Also check the plug that goes into the back of the port on the rear bumper. Corrosion can get in there and cause a short as well. Last but not least, I have heard of a few cases where that plug housing assembly it self has an internal short and has to be replaced.

The lesson for today is DON'T BUY CHEAP FUSES! I went back and verified everything today. No grounds from pin F or on the fused side of fuse 22 (TRLR PRK 15 amp). I moved the trailer harness around a bit where it passes between the frame and the gas tank. I was worried that when I installed the S&B 62 gallon tank a couple of years ago I might have pinched the trailer harness but it was all free. So I tried another 15 amp fuse and no further issues but then again I could never find any resistance to ground on the Fluke meter to begin with. When I went back to check the fuses from the extras that I keep on the truck I happened to notice a 10 amp fuse and discovered something interesting. Look at the pics below. I ran down to Carquest and picked up a bunch of 15 amp fuses. The 15 on the left is from Carquest, the middle is the 15 amp that I had and the 10 amp is also from my stash of extras. Even though the middle one is showing 15 fuse link is much smaller that the 10 amp or the new 15 I got from Carquest. I'm more likely to believe this is supposed to be a 1.5 amp but you can see how it is labeled. How the trailer lights ran as long as then did on the old 15 amp fuse I will never know. All I can think is the rain on the trip back on Saturday has some effect on the circuit. Dean

 

[2004LB7]

Good find. But I don't think there is a 1.5A fuse in that size. So, more likely a China knockoff

 

[Dean E]

Good find. But I don't think there is a 1.5A fuse in that size. So, more likely a China knockoff

Very likely. I might end up going thru the trailer lights again to make sure there is no issues there again. I did pull the spare tire down to look at the camper connection and could not see issues there. The trailer really does not pull anything power wise. All LED except for the license plate light which is a small peanut bulb. A big thanks for everyone's help! Dean

 

[1FastBrick]

Damn Chinese and there Chinese games.... ?

Just like the Dorman master door switch for my LLY...something in the circuitry is different from the OEM. It triggers the light so you know the door is open. How ever the AMP steps stop working shortly after that. I was chasing wires and connections and couldn't figure it out.

Took the original apart and cleaned it up makeing it functional again. Now the steps work... also pissed me off that it wouldn't stay in the bezel. Every now and again you push down on the window switch and the whole thing would drop down....

 

[Dean E]

Damn Chinese and there Chinese games.... ?

Just like the Dorman master door switch for my LLY...something in the circuitry is different from the OEM. It triggers the light so you know the door is open. How ever the AMP steps stop working shortly after that. I was chasing wires and connections and couldn't figure it out.

Took the original apart and cleaned it up makeing it functional again. Now the steps work... also pissed me off that it wouldn't stay in the bezel. Every now and again you push down on the window switch and the whole thing would drop down....

Don't have much experience with Dorman other that the torquer motors for the temp controls on my old 09 Impala. They are plastic and with age will start stripping the gears inside the plastic case. One of GMs more brilliant designs. Even rented a new Denalli Yukan XL that I took the family to CA for Thanksgiving a few years ago and I could hear one of them clicking away shortly after staring the XL. I ended up replacing all 4 of them with Dorman units and did not have any issues with them. There are certain things that I make certain to use quality parts with. Brakes and suspension items are certainly one of those. Really surprised to see something as simple as a mini fuse that has issues like what I experienced, but like just about everything else, you get what you pay for. Lesson learned! Dean

 

[1FastBrick]

Don't have much experience with Dorman other that the torquer motors for the temp controls on my old 09 Impala. They are plastic and with age will start stripping the gears inside the plastic case. One of GMs more brilliant designs. Even rented a new Denalli Yukan XL that I took the family to CA for Thanksgiving a few years ago and I could hear one of them clicking away shortly after staring the XL. I ended up replacing all 4 of them with Dorman units and did not have any issues with them. There are certain things that I make certain to use quality parts with. Brakes and suspension items are certainly one of those. Really surprised to see something as simple as a mini fuse that has issues like what I experienced, but like just about everything else, you get what you pay for. Lesson learned! Dean

It's all good, unfortunately the master window switch is no longer available for my truck. It was my only choice considering what people wanted for used ones... I should have taken mine apart to begin with. However, some times it's just easier to replace a part like that when time is a factor... fortunately I kept the old one just in case.