marcz62

I have looked at a lot of posts and i don't think I have seen one about this. i know i can't be the only person that wants to use the interior lights of the trailer when the truck isnt running. I'm sure some of you have run into this also. So I would like to know if anyone has come up with a work around other than a flashlight or lantern. I have a pace 5x12 enclosed utility trailer with brakes and back up battery. My truck is a 2010 lariat screw w/ 5.4 and trailer package with an aftermarket trailer brake, not the integrated one. Everything works correctly, and it was the same way with my previous vehicle. I was thinking of rewiring the lights into the backup battery but i would like to make sure that there might be an easier way first. If you guys have any ideas I would really appreciate the help. Thanks.

Watt-maker

I believe the back-up battery you are talking about is the safety disconnect for the electric brakes. If that is the case, I wouldn't recommend using that for the lights.

It sounds like everything on your truck is working ok. Ford just has the 12v on the trailer connection that way.

So, you can do one of two things or do them both. You can add a dedicated battery to the trailer that is just for the interior lights and tie it into the charge line so it recharges when your truck is on.

You can also trace the trailer pkg wire loom to the front of the truck where the charge line goes into the fuse box. Cut the charge line then add a piece of same gauge wire towards the battery. Somewhere close to the battery + terminal add either a 30-40 amp circuit breaker or a 30-40 amp fuse and fuse holder rated for the same. Connect to the + terminal of the battery. Like this, the 12v charge line is hot all the time (like gm and some others) effectively powering the trailers lights whenever you need them. The bad thing about having a constant charge line is, if the trailer plug has trapped moisture and/or corrosion it can drain your truck battery even when there is no trailer.

bubbabud

The easy fix is just remove the "TTpower" relay from the power dist bbox up by the radiater and replace it with a short jumper wire then the power to the 7 pin will be hot all the time and you can remove the jumper and replace the relay any time Oh and this will leave the 30amp fuse still in the cirquit.

willieboy

It sounds like your trailer battery has a diode on the hot line to make sure it only runs the trailer brakes, and charges. You could remove the diode and replace the battery with a larger one, and then be fine. This is essentially how every Travel Trailer is setup, so no doubt it will work well.

brulaz

On my TT (and I thought most trailers?) they are the same. So when boondocking without shore power, we *are* drawing down the safety disconnect battery for the electric brakes. Obviously you don't want to completely draw down the battery ... But it should charge back up later when connected and on the road.

Watt-maker

True, TTs are like that but utility trailers and small enclosed trailers just have a real small battery just for the brakes. I'm just guessing at what he's got.

smokeywren

My cargo trailer has only an itty bitty 12-volt battery on the trailer tongue, and that battery is used only to lock the trailer brakes if the trailer gets disconnected from the tow vehicle. All other electric circuits are powered by the 7-pin trailer connection to the tow vehicle.

If you want the lights inside the cargo trailer to work when the trailer is not connected to the tow vehicle, or if connected but the tow vehicle is not running, then you need to replace that itty bitty battery with a much bigger 12-volt battery, then rewire the trailer so the interior light circuit is powered by a hot line that goes directly to the battery through a fused link.

This is much easier if you have a wiring diagram for the trailer. If you don't have a wiring diagram, then you must trace the hot and ground wires from the switch back to where it joins up with the rest of the wiring harness. Disconnect the two wires from the wiring harness and re-route them directly to the terminals on the battery. If the wires are color coded, then you may be able to just note the color at the switch and find that same wires at the wye ("Y") in the harness where that pair of wires join the rest of the harness.

Disadvantage is if you leave the lights on in the trailer, you will discharge the trailer battery down to fully discharged, which will ruin an ordinary 12-volt car battery. One fix it to use a deep-cycle marine battery instead of a car battery, but the marine battery will probably cost at least twice as much as a car battery. I use the Optima blue-top marine battery in my RV trailer for just that reason, but it costs about twice as much as the Optima red-top car battery. Recently I saw the blue-top at Sam's Club for around $250.

Here's a "cheap" marine battery from Northern Tool. Only $320:
http://www.northerntool.com/shop/too...0376_200390376

bubbabud

just jump the relay like i said earlyer total cost a 2 inch length of 14 gauge wire completly safe and completly revesable in about 10 seconds time and you will have power to the trailer any time its pluged into the truck. only down side is if you go off and leave the light on for 2 or 3 days you could run the truck battery down.

tomb1269

If you are looking to add the battery option but with less expense look in to using a jump pack (the battery packs that you jumpstart the cars with). A lot of guys that build their own tear drops and ttt use this method when they are looking for a small and cheap battery source for lights as you are.

marcz62

Thanks to everyone being so helpful. I like the idea of jumping the relay. I don't use the lights inside all that much and they are two led lights that draw very little. And honestly I rarely would ever use the lights with out the trailer being hooked up, and I always drop the trailer if I'm not going to be on the road the next day.

But it does scare me to be taking a wire and replacing a relay. What does that relay actually do?

I have another question for all you experts and I should probably start a thread, but when I am towing my trailer at night with my lariat, if there is a car behind me with bright lights my trailer obscures the sensors in my rear view mirror and my side mirror will not dim. Wow I love having a dimming side mirror. Has anyone found a work around?