Parasitic power drain

J Whisenant · May 9, 2022

Hey new guy here.

I have a 2015 Silverado 2500HD with a 6.0 gas engine with 130000 miles. It does have the integrated trailer tow package on it. A few weeks back I had a car trailer connected to the truck and noticed the right trailer turn/taillight was on without the truck on or headlights on and no key in the ignition. My first thought was bad trailer wiring. So I disconnected the trailer and using a test light at the seven-way trailer plug, found that I had power on the right trailer turn/taillight pin on the truck trailer socket. Next, I took the plug apart from the back and tested the USCAR plug from the truck to the trailer socket and it had power on the right trailer turn/taillight pin. I then went to the fuse box under the hood on the driver side and located the number 17 fuse witch is the right trailer turn/taillight fuse and it had power on both sides. So I pulled the fuse and the power at the rear bumper was gone. The truck sat in the yard all night and the next day until I got home from work when I tried to start it and the battery was dead. I jumped it off and it ran fine.

So then, I went to one of the auto parts stores and had the alternator and battery checked. Both were good, the battery was weak but I live only two blocks from the parts store so it probably did not have enough time to charge. The battery was about three years old so I went ahead and replaced it just to be on the safe side. I needed the truck to tow a vehicle out of state so to make the trip we disconnected the negative cable on the battery when we stopped and the truck ran fine.

Since then I have checked every plug that is at the back bumper, the trailer brake module, the trailer relay in the fuse boxes. This weekend using a voltmeter I pulled every relay and fuse one at a time in all fuse boxes and the only time I made a difference in the meter and the test light was when I disconnected one of the power cables coming directly off the battery. One thing that I did notice was, at one point I had 12.60 volts at the back of the truck in the trailer plug. Now I have 3.56 volts and the voltage at fuse 17 has dropped to match the trailer plug. Also, I noticed that before when I disconnected the battery the test light on the fuse would simply go out instantly now it fades out as if it is getting its power from a Retained Accessory Power source.

So if any of you have any ideas please chime in. Oh and I have spent lord only knows how many hours digging and looking for an answer on the net but sometimes it takes a fresh set of eyes. Thanks.

Edited May 9, 2022 by J Whisenant
Better to read.

swathdiver · May 9, 2022

Electrical gremlins are not my strong suit but if yours were mine I would get hold of a bi-directional scan tool and run a parasitic draw test.

If you can edit your post and break it up into paragraphs you'll get more responses, that hurt my eyes!

J Whisenant · May 9, 2022

Thanks for the advice.

J Whisenant · June 15, 2022

I am still working on this and have been in touch with a couple of mechanics that believe my problem is coming from a bad circuit board that is under the main under hood fuse box.

So I have been looking for a place to buy one and I am not having much luck. Does anyone on here have a source for one? Any help would be greatly appreciated.

Thanks.

J Whisenant · June 22, 2022

Ok so I think I have this solved. I replaced the main under hood fuse / relay box with a new one yesterday and checked for voltage at the trailer right turn signal fuse and I had no voltage whereas before I had power at that fuse all the time, even when the truck was not running.

Hope this helps someone. The part was only a couple hundred and came with all relays and fuses. Just make sure you order from a place that requires you to provide them with the VIN. Number.