Is this OK...or is it bad?

Overnight stay in a parking lot or campground, all I do is drop the front gear to help steady the trailer. I don't bother unhooking the pig tail.

Hastey said:

That's just what I said, the A/C current from your shore hook-ups cannot get to your tow vehicle. The 12VDC "battery tender" will not let any A/C current to your TV. Even if you are not connected there is 12VDC to that feed from your truck. In fact this is the same feed that I tapped into that runs my transfer pump for fueling my equipment around the farm from my aux tank and it is live all the time.

Now just so you know I'm not just talking out my rear, and btw I am in now way trying to be a smart-a## either so please don't take it that way. Take your multi-meter or testlight out and check your 7-pin without anything hooked up or on. With the truck off you will have 12VDC there at the Aux Pin. With your trailer hooked to 30/50 amp check your trailer connection and you will have 12VDC there to. So backfeed or not you are only adding 12VDC to a 12VDC system. JMHO

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Hastey,
I don't mean to derail Rodbusters question. I'll agree with you that with everything working normally, that if you have 12.0 volts both from the truck and the RV, you have no current flowing either direction through the pigtail connector. That's simple ohms law.

If you are plugged in to shore power that is not the case however. The convertors in most of our RV's are capable of delivering 60+ amps. The voltage is also determined based on which mode the convertor is in. For instance, the Progressive Dynamics 9200 Series provides 4 modes of operation; BOOST, NORMAL, STORAGE and DESULFATION modes which can deliver just under 16 volts. Probably not recommended by your vehicle manufacturer, but still none of that should be any problem.

I've also been victim of a nearby lightning hit that ran in to our RV via the shore power (at RVacation in 2007, in fact) connection, that caught a surge suppression power strip on fire 3 hours later and a television to die 2 days later. I realize that is on the 110v side of the convertor, but I'm glad my $65k truck wasn't plugged into anything at the time.

My advice stands, and anyone is welcome to take it or leave it. Disconnect the pigtail, as it serves no practical purpose when you are on shore power, it takes 30 seconds.