Wire question

[RandyH]

My cargo trailer has two interior lights. The hotwire from both are spliced together, then the single wire is run to a junction box that contains wiring to the trailer plug. I want to run these lights from my onboard battery. Can I just clip the wire in the junction box and put a piece of heat shrink tubing to protect the wire. It s a larger gauge black wire.
Thanks,
Randy

[tony.latham]

My cargo trailer has two interior lights. The hotwire from both are spliced together, then the single wire is run to a junction box that contains wiring to the trailer plug. I want to run these lights from my onboard battery. Can I just clip the wire in the junction box and put a piece of heat shrink tubing to protect the wire. It s a larger gauge black wire.
Thanks,
Randy

One wire goes to the + side of the battery and one goes to the -. But whatever you do, fuse the + wire with the appropriate sized inline fuse. (Which is base on whatever gauge that "larger gauge" wire is.)

I guess the question about your question is where does the lights ground wire go?

A lot of us run everything through a marine fuse box like this one:
https://www.amazon.com/Blue-Systems-Bla ... HQ0CQ?th=1

But the hot wire to this box also has to have an appropriate inline fuse too.

Tony

[McDave]

Hey Randy,
Obviously this is not the most complicated circuit. I'm guessing the "hot wires" coming from the light fixtures are 14 ga. and the "larger gauge black wire" is 12 ga.
So, black is typically positive, White neg or to ground. If the fixture has a on/off switch, then all you need to do is install a inline fuse on black wire then to positive of battery. If there are no on/off switches on fixtures you will need a switch after the fuse on black wire. A terminal block would be good place to start, unless you are planning a power center like PD-4045 or a WFCO 8955 or similar. That way you don't have to attach a bunch of wires to battery post. The unit suggested by Tony would work fine. If you think you will want a power center system in the future, then I would just run lights to battery temporarily, inline fuse, switch if needed, then to lights.
Battery negative must run to chassis/frame, a good clean (to metal, not paint etc.) tight connection.

McDave

[RandyH]

I guess I didn't make myself clear. I just wanted to know if it would be okay to clip the hotwire in the junction box at the front of the trailer. From the 7 pin diagrams I've seen, I understand the black wire is typically for aux power. The lights black wire is connected to this one; nothing else is connected. I want to cut the lights here and run the circuit to my onboard battery. OK?

[ffemtp]

I guess I didn't make myself clear. I just wanted to know if it would be okay to clip the hotwire in the junction box at the front of the trailer. From the 7 pin diagrams I've seen, I understand the black wire is typically for aux power. The lights black wire is connected to this one; nothing else is connected. I want to cut the lights here and run the circuit to my onboard battery. OK?

You should be ok to do that. There are a couple of things to consider however. 1) is that wire providing power to anything else (or will it in the future in case of any new mods)? 2) if you cut it, ensure you protect the cut wire and leave it so that you can reconnect it in the future if necessary, 3) have you considered just running a new (fused!) wire from the positive side of the light to your battery?

I hope this helps...

[McDave]

OK, I could be wrong, but I think the black aux power wire from 7 pin should also run to positive of on board battery. If we are talking about the little battery usually mounted outside on the tongue from factory that is only used for trailer runaway brakes? Otherwise you would likely have a dead battery when you needed it most.
My trailer is single axle, no brakes. Came with 4 pin connector. No battery. The truck running lights had to be on to make trailer dome lights work. I had to upgrade wiring to 7 pin so truck would charge trailer battery, (125 ah deep cycle), and power refrig. while in transit. Power comes from a "keyed" circuit in truck so that trailer can't feed off truck when truck ignition is off. Also, I added reverse lights on trailer and added that circuit to be activated from truck reverse light switch.
So, I guess to answer your question, It's your trailer. You can cut any wire you want. But as tony said, leave enough wire to repair it when you figure out you didn't really want to do that. And of course, always terminate and insulate any cut or bare wire.

McDave

[RandyH]

ok, good, I just wanted to make isolate the inside trailer lights from the tow vehicle...

[troubleScottie]

The issue may be that you want a second inexpensive junction box.

Depending on the size of your system, you have 3 sets of circuits: the trailer lighting - brakes, turn signal; DC circuits and AC circuits. Obviously you need at least the trailer lighting. Personally, I would leave the trailer light junction box alone.

A lot of people have large complex systems like power distribution panel with AC and DC circuits, circuit breakers, fuses, shore power connector, and even converters for charging the battery. Given your stated needs, overkill.

The other end is a simple fuse block like the blue Sea 6 position fuse block, about $30. It is small, just screw to the wall. You connect your second battery to one end and run wires from the other side of the fuse(s) to the device(s). The return/ground goes to a common bus bar on the fuse block which then connects to the battery ground. Very inexpensive, and very safe. Fuses are always good even for such simple relatively safe. Assuming you have a switch on the light, you're good. You even have space for expansion. In addition, everything is inside the trailer, no extra holes, etc to deal with.

The only addition is a switch between the battery and the fuse block. Again a safety feature. Good if you really want to make sure nothing is on.

[Wolfscout]

seems to me with the price of some of the lights being less than $10 bucks on ebay, you could simplify the problem by just installing new lights and wires that run separate from the tow vehicle to your on-board battery. LED ones cost more but they are so worth it. Most interior lights on the new trailers I've looked at are not LEDs. Even the one I started my newest project on did not have LED lights ( they all are now).

[McDave]

Here is some handy wiring info. If you look at the color chart it shows Red or Black for 12 volt power in to trailer interior lights, breakaway switch, and battery charging.
https://www.etrailer.com/faq-wiring.aspx
Go out to the tow vehicle and check the black pin (probably top right) with the key off. There should be zero volts between pin and ground. Then start the truck and check again, should read 12-14vdc+ This should provide the isolation you are looking for.
You could also just disconnect the trailer from truck at 7 pin when not in transit. This is known as the K.I.S.S. method.
Probably a good practice anyway.

McDave