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From: Ted Heise <theise@panix.com>
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Charging from tow vehicle
Date: Wed, 5 Mar 2025 22:11:31 -0000 (UTC)
Organization: My own, such as it is
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On Wed, 5 Mar 2025 20:03:57 -0000 (UTC),
  Ted Heise <theise@panix.com> wrote:
>  On Wed, 5 Mar 2025 09:05:19 -0600,
>    sticks <wolverine01@charter.net> wrote:

> >  The first place to start would be the 7 prong plug in, on the 
> >  tow vehicle, and the vehicle being towed.  I am going to take 
> >  it for granted most of us would be using a 7 prong plug.  
> >  Any differences are minimal and easily solved.

> >  So let's start on the tow vehicle.  It might surprise some of 
> >  us that our plugs don't even have power in them as delivered 
> >  from the factory. I have an F-150 and was quite surprised 
> >  myself that I had to install an additional fuse to get my 
> >  line hot.  It was wired, but not fused and inactive.  With 
> >  today's CANBUS systems, it can be difficult testing this, and 
> >  you really have to use a 12 volt test light and not a volt 
> >  meter.
> 
>  My thinking was to take a reading from the LiIon battery app 
>  with the battery connected to the trailer and then with the 
>  fridge started (I think it may run off the batt for a minute or 
>  two). Then I would connect the 7-pin to the running TV and 
>  repeat these readings.  Does that seem like a reasonable 
>  approach?
> 
>  I need a block of time to get out to the storage unit for this, 
>  so in the meantime I figured I'd take some measurements at the 
>  7-pin. First I connected clips from my multimeter with the TV 
>  off.  Surprisingly, I got some sparking, may have been from 
>  touching across pins.  But once I had a good connection I got 
>  no voltage.
> 
>  Now this could be from the line not being hot (e.g., because of 
>  a fuse needed), or because a multimeter won't work.  But I 
>  vaguely recall having gotten a 12-13 V reading from the pins 
>  some time in the past.  So maybe the sparking blew the fuse.  
>  I'm trying to run down where that would be and will let you 
>  know what I find.

Okay, I found the fuse (designated "trailer battery") and found it 
was definitely blown.  Put in a replacement, and still get no sign 
of 12 V at the proper pins (at about the 1:30 and 7:00 positions).

So I guess next is to ask the dealer to look at it.

Might look for a test light too, I guess.

-- 
Ted Heise      <theise@panix.com>       West Lafayette, IN, USA