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lensnel 12-31-2018 11:26 AM

Trailer batteries not charging while driving
I have a problem with my Tow Vehicle. There is supposed to be a constant
12 volts to provide trickle charge for the trailer batteries. My 2015 Silverado HD Duramax shows no voltage on pin 4 while the truck is running. Does anyone know where the fuse is for that pin? I cannot locate it on either side of dash or under-hood fuse boxes?

Creeker 12-31-2018 12:03 PM

On the older Duramax trucks it was under the hood. It was not like a regular looking blade type fuse but a larger black square looking fuse. The fuse installed from factory in that position was actually a blank. It required removing the blank and installing with a true fuse. Again, it didn't look like a regular blade type fuse.

I'm going off memory and this was on my previous '07 Duramax. I'm thinking it was in a corner position of the fuse box but this was 11+ years ago and I can't remember what I had for breakfast this morning. :D

scottz 12-31-2018 01:03 PM

That is good advice. Ford did the same thing with my truck. The relay for that circuit was not installed, I found it in the glove box and had to plug it in myself.

lensnel 12-31-2018 02:21 PM

It seems in '07, that was the case. I was hoping to hear from someone with a newer truck that has/had this same problem. A photo of the fuse/location would be great. My dealer is no help so far... still waiting for them to provide an answer.

Fish 12-31-2018 05:13 PM

This says post2 on the driver side of the vehicle under the hood.

lensnel 01-01-2019 01:35 PM

This forum is the best and the wealth of knowledge here is boundless. Thank you for your help.

Fish 01-01-2019 08:30 PM

I kind of had a head start. I traded in a 2015.5 duramax ccsb 4x4 on my Ram. I had a problem blowing fuses when I pulled my flatbed trailer, didn't have any lights or brakes or turn signals. I actually printed that diagram out and kept it in my glove box.

cgeis48 01-06-2019 03:15 PM

Don't do this if your battery goes dead
I had a dead battery after dry camping for two days. I couldn't put the slides in on the trailer so I backed the truck up and plugged in the RV seven pin connector for a few minutes. Then I pushed the button to retract the trailer slide that was a mistake because it blew the fuse. I figured that is what happened so, I went to a Ford dealer in Colorado Springs. He charged me $125 to change the fuse saying it was necessary to inspect the entire electrical system. To this day I think it was BS.
A fellow Montana camper had a loose battery in his trailer compartment so we used it to jump the trailer hydraulic pump to put the slide back in.

Ricos Ride 01-06-2019 04:01 PM

It’s easy to tell if the trailer fuse is installed. It’s in the fuse box under the hood, near the brake cylinder It is a pink rectangle, 30 amp fuse. My 2015 Silverado 2500 did not have the fuse installed from factory. My 2018 Denali 3500 came with fuse installed.

SaraLena70 01-06-2019 04:21 PM

The first thing you should do is check for 12 volts on the charge terminal with the tk ignition switch on. The charge terminal is normally marked on the cover of the connector.

speedster100 01-07-2019 08:31 AM

It is in the fuse box under the hood, it is a microfuse type small rectangular and on my 2015 it seemed to blow if I plugged in the connector cord from the rv to the truck while the trailer was still plugged into shore power. If I waited until I unplugged from shore power I never had an issue... It will be your issue. Check the bottom of the fuse box lid as it will identify which fuse it is.... good luck

RichardD 01-07-2019 10:42 AM

2 Attachment(s)
Been there, done that!
We have an early 2015 (Mfg 2014) Chevy 3500 that we experienced the same problem with. These 2 attached pictures should help you find and identify the 30amp fuse in the fuse box under the hood. Most auto parts stores do not carry this type of fuse, I purchased a few extra from a Chevy dealer to have spares. I have used one of my spares for my truck and a second spare went to help another RVer with the same problem.
What causes the fuse to blow is when you have low voltage in your 5th wheel batteries and than connect your truck to the 5th wheel and you activate the hydraulic motor. This motor pulls more than 30 amps which it can't get from your coach batteries so it tries to pull it from your truck and than blows the fuse.
Lesson learned, don't run your hydraulic motor or any item that pulls more than 30 amps when your coach batteries are low on voltage while you are connected to your truck.

Another lesson learned! If you try to run your hydraulic motor with low battery voltage you will eventually burn up the motor. It is a very expensive motor!!!

I hope this helps.

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