Warning ! Problem with 2015 Chevrolet & Tahoe Suburban Toads

If the negative battery terminal is disconnected, where is the car getting the +12 from to reference to the coach ground?

With direct current the circuit has to be completed back to the source. If the negative to the car/truck battery is disconnected how is the current returning to the battery? I agree that there is a ground to the coach through the attachment of the toad wiring, but as mentioned above, where is the current coming from? Maybe through the coach batteries, but this has nothing to do with the toad battery. If this is the case the same problem would exist disconnecting the positive or both. Maybe I am confused, but I believe this is the way DC current works.

All I can think of is this scenario:

If you're supplying power to the truck's brake fluid pump, lights and other systems, that power will back-feed into the body / engine computers controlling those systems, and since those computers are grounded to the chassis, which is now grounded to the coach via the tow bar, you have a complete circuit.

I don't see how disconnecting any of the truck's battery cables would help with that scenario.

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.

"msturtz"......Your warning has some merit, but your explanation has some issues. If you disconnect the negative battery cable and do nothing else, there is NO WAY for the toad to get power to the computer. You could hook a hundred ground wires to the chassis, it's still not going to complete the connection (circuit) across the battery.

Here's what I think you're trying to say. If you disconnect the negative terminal on the battery and then INSTALL a 12 volt toad charging system, to charge the toad battery while driving, you could power up the toad inadvertently by back feeding through the connections. The problem is....you don't need a toad charging system if the battery is disconnected, it won't be drained by anything.

What you need is a connection from your coach to your braking system if it requires power, like a Brake Buddy or other brand. It needs to be connected separately to the coach, not via the toad battery.

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."

If you disconnect the battery (either negative or positive) why do you need a charge line?

Well I was wondering this very point myself yesterday. Traded my '13 Silverado yesterday for a '15 Silverado 2500 and the new Owners Manual indicates to disconnect the negative battery cable. I am a little disappointed that it is now not as easy to tow the new GM vehicles as we need to disconnect power every time.

I am going to try and figure out how to get a disconnect wired that it can be done under the dash from the driver's seat.

Guess it's back to work to figure it out.

Big honkin' continuous duty relay in battery cable with toggle switch on dash to activate it. I would use a normally closed relay, if it was me.