msturtz wrote:
The issue is simple. All the electrical equipment in the towed vehicle is tied to the hot and negative side of the towed vehicle. Also with most motorhomes the charge line is connected to the chassis battery. So disconnecting the negative line won't work for several reasons. As soon as you connect the motorhome to the towed vehicle you now have multiple ground paths to the battery that bypass the main towed vehicle ground. However it isn't quite the same with the hot side. If you isolate the towed vehicle hot connection you won't have any way for the vehicle system to power up. The only power which would be present from the battery would be the direct connections from the components that require power to the battery which would vary depending on the braking system. The lights are usually powered by the coach. GM was technically correct but failed to account for the vehicle in actual use behind a motorhome.
Here we have the crux of the problem. There is an installed charge line. If there is an installed charge line, you need to disconnect the positive side of the car's battery, not the negative side.
Your original post failed to mention that this scenario only occurs with a charge line installed, hence the confusion.
BTW, "most" motorhomes don't come with a charge line installed. It is a consumer add on. The reason it is a consumer add on is that it is installed on the car. "Most" motorhomes may have 12v power to the 7 pin outlet, but without the wiring installed on the car, that power goes no further.
Your thread should be titled "WARNING: Problems with toads when installing battery charge line."
