12v circuit questions

Hello! I've been remodeling my 1995 Jayco and have run into a problem.  I removed the radio and the cabinet over the bed. Both ran on 12v and since then the lights have not worked in the back half of the trailer, even when plugged in to 30amp service. I know I broke the circuit but I'm wondering how to close the loop when you don't have a "fixture" to connect the black to the white.  I don't intend to replace the radio or the lights.  I've searched the internet about 12v systems and how to "terminate" the loop without a fixture of some sort and have come up empty.  Any help is appreciated!

PS, when I just connected black to white with a wire nut, I blew the fuse for that part of the trailer. 

Thank you in advance!
Kristen

You do not need to connect the black to the white and as you can see it will blow fuses.

The question is how to reestablish the loop without a device or fixture to bridge between black and white. 

It is not a loop, it is a dead end. I don't know what you did not interrupt the circuit, but it wasn't removing the radio.

The "loop" closes through each and every fixture on the hot lead, i.e. they are wired in parallel. The ground side of the fixture makes (closes) the loop for each.  In typical trailer wiring, the fixtures are connected to a common ground wire which in turn terminates by connecting to either the trailer chassis (which is grounded to the battery negative) or directly to the battery negative itself.  Typically there will be a terminal strip wired to the battery negative and the 12v ground wires from various areas of the trailer will connect there.

I suspect you interrupted one of the common ground wires when you removed the radio.  If the ground wire came to the radio and continued on, you probably need to connect the ends of that wire together so that it continues to conduct electricity. Do not connect the hot and ground wires together - that's a direct short.

Be aware that you cannot assume black & white wire colors for 12v power - there is no recognized standard color code as there is for 120vac wiring.  You need to identify which wire is the ground side of the circuit.

krstylor said:

The question is how to reestablish the loop without a device or fixture to bridge between black and white.

Click to expand...

The "Loop" was not established by those devices or fittings unless there was more than 2 wires to one or both of them. If there was, then black to black and white to white should do it.  The only way to fix the problem as described will be to trace the wiring associated with the now non working circuits and see what is open. (Maybe another, perhaps inline and hidden, fuse somewhere??)

It's not a loop, think of the wiring more as a railroad track with a pair of wires starting at the fuse panel and running to each fixture fed by the circuit.

One wire carries the positive voltage, the other wire completes the negative circuit back to the battery.  Each fixture is connected across the wires allowing current to flow from positive to negative through the device.

At the last device the wires just end.  There's nothing connecting positive to negative except for the devices on the circuit.

A direct connection from positive to negative is called a short circuit because there's nothing to slow down the current flow, electricity just takes the short cut to get back to the battery.  This draws more current than the wires can handle without overheating so the fuse blows to interrupt the flow.

Any break in either line will stop current flow to everything further down the circuit, just as if you opened a switch.

Since you made changes at the cabinet containing the radio, this is where I would look for missing connections.

One thing you can do to prevent blowing fuses while you're troubleshooting is to temporarily replace the fuse with a light bulb using a couple pieces of wire to connect the bulb to the fuse terminals.  The light will glow dimly along with another bulb in the circuit when one bulb is turned on.  If there is a short circuit the fuse bulb will glow at full brightness while limiting current flow to a safe value.

This lets you test connections without repeatedly blowing fuses.