Originally Posted by Vinnie
We had a battery selector/cutoff switch installed on the trailer a red dial that let's you select battery 1 or 2 or both or off. Is that the same as a battery isolator and if so instead of unplugging the tow vehicle you would just dial the batterys to off?
Yes it would do the same thing, I guess, but my point is that the switch must be automatic, not manual.
What I installed is this thing:
Tow Ready - Battery Soleniod
I added this solenoid in my Toyota Venza in series with the wire supplying the +12V to the Aliner. One wire goes to the battery. On wire goes to the trailer. The third wire is connected to accessories, like the +12V socket in the back of the car. The casing of the solenoid is connected to the frame, so the - pole of the batterie.
When the car is turned off, the accessorie is off and the solenoid disconnects the TV and the trailer. That way the trailer cannot drain the starting battery of the TV. When I turn on the car, the accessories goes to +12V, and closes the solenoid contact and the TV can feed power to the trailer. When that happens, the motor is running and I know that the battery of the car is being recharged, so it is OK to recharge the trailer as well.
The only drawback is that if I let the car on accessories only with the engine not running, then the car batterie gets drained into the trailer. I refrain from doing that. In a perfect world, I would connect the control terminal of the solenoid to the ignition signal instead of accessories. That way the current from the TV would flow to the trailer only when the engine is running.
Doing the switching manually like you suggested is prone to 2 errors.
a) forgetting to disconnect when you stop at the grocery store: you drain your vehicule and cannot start the engine. Not funny.
b) disconnecting when you stop at the grocery, but forgetting to turn back on when you leave the grocery parking: you get spoiled food. Furthermore, the emergency brakes work on the trailer battery. So forgetting to turn it back on is REALLY dangerous.
15.95$ really well spend for a solenoid, AFAIK.