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Old 06-29-2010, 08:00 AM   #1
Bex
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Trailer battery feeding back to TV?

Hi folks
I had a vehicle mechanic "Guy" that bartered my service for his. He installed my BK. He did not splice the brake switch wire, but my cousin and a freind of his (a vehicle mechanic) fixed that.
He installed the 12v feed to the trailer battery pin and the power supply to the P3 controller on the same ignition outlet on the "firewall" (new term I just learned for fuse box). Two spade connectors, one for each now take the place of the ignition fuse and the 12v feed has the fuse.
Now, when the TV is started or even when the key is inserted and turned, the fuel pump starts to operate. When the vehicle is started, it runs, everything works as it should (P3 included) but the TV will not shut off without first pulling the 12v feed.
My questions:
1. How do we take the 12v feed from the ignition on the "firewall" without it affecting the way the vehicle operates, ie isolate the 12v feedback from the trailer, if indeed thats what is going on?
2. Currently, the fuse is on the 12v, should it be changed over to the P3 or whilst the two are plugged into the same IGN is/was this one fuse enough to keep the P3 safe??
Thanks for any help here

Bex
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Old 06-29-2010, 12:13 PM   #2
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It is customary to connect the 12 volt feed line to an unswitched source of 12 volt power in the tow vehicle. This prevents the problem with the engine running, and also reduces the amount of current flowing through the ignition switch in the tow vehicle.

It is also customary to connect the 12 volt feed line to the brake controller to an unswitched source of 12 volt power. This is to ensure that brakes will function even if the ignition switch is off.

Opinions vary on fusing for brake controllers. There is a school of thought that maintains that it is, overall, safer to run brake controllers unfused because a blown fuse would cause a loss of trailer braking. There is also a school of thought that the fire hazard is greater than the hazard from loss of braking.

I use a self-resetting circuit breaker.
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Old 06-29-2010, 01:05 PM   #3
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towing option

this situation, of course is why having a towing option on the TV is nice, if not almost a necessity. Making stuff work correctly with a relatively new TV is not as simple as Wally would like. As indicated, there are a lot of issues to consider. Allowing too much current flow through the ignition switch, or any other componenet is a disaster in the making. Emergency flashers are another bug-a-boo, they should work on the TV as well as the trailer, when needed. As well, the trailer battery should NOT feed back into the TV, that situation can just lead to dead trailer batts, or worse, some component in the TV energized while parked, causing premature failure.

Most TV's set up with a towing package have relays activated by the TV that allow all functions through the 7 pin to the trailer to operate correctly. A good trailer shop or RV shop should be able to wire the unit(s) correctly. Pay attention to the battery charging lead size if you expect the TV to recharge the trailer batts while towing; usually, it needs to be up-sized. Battery isolators may be required for this.
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Old 06-29-2010, 06:09 PM   #4
Bex
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Thanks!
I am going to install a fuse on the power feed to the P3. Can I leave this plugged into the current 12v source marked, IGN?
Can I leave the fuse on the 12v feed to the battery but plug it into any other available 12v source?
IS there any point in leaving this fuse in place?

Bex
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Old 06-29-2010, 06:44 PM   #5
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Quote:
Originally Posted by wmarsha View Post
this situation, of course is why having a towing option on the TV is nice, if not almost a necessity.
It's not that hard for people who are familiar with 12 volt wiring. The factory wiring on my K2500 was badly butchered by the previous owner, so I redid it from scratch. It took two hours, no big deal.

Quote:
As well, the trailer battery should NOT feed back into the TV, that situation can just lead to dead trailer batts, or worse, some component in the TV energized while parked, causing premature failure.
I don't believe that's true. Most installations, including many if not most factory trailer wiring packages, leave the charge line connected to the TV battery continuously. The only real problem with this is that you can drain the TV battery by running the furnace all night and end up with a truck that won't start. Most people know this and just unplug the cord when that sort of thing is, potentially, a problem.

Quote:
Most TV's set up with a towing package have relays activated by the TV that allow all functions through the 7 pin to the trailer to operate correctly. A good trailer shop or RV shop should be able to wire the unit(s) correctly. Pay attention to the battery charging lead size if you expect the TV to recharge the trailer batts while towing; usually, it needs to be up-sized. Battery isolators may be required for this.
Usually, only a relay for the tail/marker circuit is necessary, plus heavy duty flashers.
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Old 06-29-2010, 06:46 PM   #6
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Quote:
Originally Posted by Bex View Post
Thanks!
I am going to install a fuse on the power feed to the P3. Can I leave this plugged into the current 12v source marked, IGN?
I would not recommend connecting the P3 to the IGN source because then the brakes will not work if the ignition switch is turned off.
Quote:
Can I leave the fuse on the 12v feed to the battery but plug it into any other available 12v source?
Yes, again you should connect it to a suitable always-on connection.
Quote:
IS there any point in leaving this fuse in place?
Yes, it provides some fire protection in the event the trailer wiring shorts out.
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Old 06-29-2010, 10:58 PM   #7
Bex
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OK so here is where I am at with this. I found an available 12v always on and plugged the battery feed into it.
I found another, separate 12v always on feed and will plug the BK into IT when I have fitted a reset breaker.
Is there a way to stop the (trailer) battery draining the TV power? Do I just need to be aware of the fact it might draw and so unplug it or the trailer, ( as already suggested) when parked?

Thanks again Guys, I really appreciate your help

Bex
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Old 06-29-2010, 11:06 PM   #8
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There are various sorts of battery isolators that the motorhome and truck camper people use. Some trailer owners use them but most don't. I don't have one, so, as you say, it's an awareness thing. In practice it's rarely a problem, at least for me, because if I'm going to be parked somewhere for several days without shore power I'll end up disconnecting the truck and driving around.
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