Short in 12v circuit

[dogfish]

I have a 1993 15' Sunline I bought last year. Everything worked then. last campout the 3 ceiling lights would not work over the rear couch. I found the fuse had blown and put in a new one which instantly blew. There's a short somewhere in the circuit. I tried to find it but can't trace the wires very far. One black wire comes out of the fuse socket and two black wires feed each fixture as well as two white ones.

I don't know how the wiring goes, the manual had nothing about this. I don't know if there is anything else on the circuit besides the 3 lamp fixtures. Other things appear to work fine. I have no clue how to find the short without tearing out walls. The wife doesn't like it when things don't work. She thinks the rv will need to be junked. Has anybody got an idea that would help?

dogfish Dan

[JohnB]

Hi Dan,

I’m on limited internet signal right now but this may help.

If you blow the fuse instantly, you are dead on, you have a short blowing the fuse.

The lights have both a hot wire (DC+) usually a black wire, and DC ground wire (DC-) negative white wire brought to each light fixture.

If you have a volt/ohm meter you can track down the area the short is in.

Try this, unhook the camper battery and unplug from shore power. You want the camper dead with no power on it.

Usually, Sunline had a wall switch by the entry for at least one ceiling light. Not sure which lights you have that are out. That switch gets its power from the ceiling lights fuse block then jumps to the light fixture. It may only be for one light, it all depends on your model, year of camper and floor plan. If you know that light did not work when the fuse blew, then that switch area is suspicious that a wire might be touching the siding and creating a short.

Next is the ceiling lights or wall fixture lights that are only controlled by the switch on the fixture . You will have to take down all those fixtures and expose the wires. There may be a worn or corroded situation where the hot and ground wire are crossed.

Before taking anything apart get your meter on the ohms scale. At the blown fuse block, remove the fuse first. Test for ohms between the downstream side of the fuse holder which has the wire on it. Test between that wire and DC negative in the fuse panel area. The white stranded wires are for the DC negative. Not the solid white wires which is 120 AC neutral. You should get a close to 0 ohms reading as you have a short. It you get high mega ohms or OL for open circuit on a digital meter and no continuity on the meter, then something is wrong with the meter etc

Assuming you have confirmed, yes that circuit wire is shorted then start testing like this

Pull the light bulbs out if all the fixtures that you know do not work. Test the black wire again at the fuse for ohms. The light bulbs if they are incandescent bulbs have low resistance through them. If you still have a dead short, and low resistance numbers then you most likely will have to pull the bulbs out of all lights including the range hood as you have no idea how many lights are in that shorted circuit .

Check ohms again at the fuse block. If it still comes up shorted, then taking wires apart is going to start. Start at the light closest to the fuse panel. Unhook the black wires, have them out in the open not touching anything. Test at the fuse panel again. Did the short go away or not?

If the short went away, you now know the wire from the fuse to the first light is good. The problem is down stream of that light, then test at that light between the black and white wire and see if it is shorted. If so, then the issue is downstream. Keep taking lights apart and testing from a know good spot until finding the short

Corrosion in the fixture can create the short between hot and ground. Or other wire crossing etc.

The wall switch can also be a possibility of getting touching the siding

They jump from one light by to the next and the wires only stop jumping when you reach the last fixture. You can tell, there is only one black and white wire at the end of the circuit or at the end of the light switched circuit

Good luck and hope this help

Camper model number helps also for future posts.

John

[dogfish]

Hi John,

Being new on this forum I somehow logged myself off, or it was an automatic logoff?
I checked my messages but there were none. I discovered I was logged off and immediately logged on a little bit ago. Anyway I didn't get your post until Sunday night 8:30. Thanks for the info.

What I know about electricity I learned myself with help from some occasional pros. My knowledge has its limits. What I did today I did before reading your post.

I unscrewed the three ceiling lights (2 were under the storage above the couch) I had them hanging by the wires, each fixture being served by 2 black and 2 whites. Why, I don't know. Wired in series perhaps? Anyway I had the idea to disconnect the 2 black wires from the one in the ceiling and tried a new fuse. The 2 lights under the storage cabinet came on! I tried reattaching one black wire to the ceiling fixture and that light came on too. Then as I expected when I touched the other black wire the fuse blew.

I isolated the problem to downline from the fixture in the ceiling without checking ohms. (I do have a couple of multimeters laying around but my knowledge about them is limited.)

The light over the sink was out and the switch at the door didn't turn any light on. I suspect these are downline from that ceiling light. I'll see what I can find about them tomorrow or whenever I can get time.

Thanks for the info you gave me John, I never associated the switch by the door. Could it be that the switch works the light over the sink? I don't know if that's a common feature or not but it would be an "Ah ha" moment. And I will look for my multimeters.

Dan

[Stubborn1]

Hi Dan! T1950 2000 here. Catching up on posts from our weekly email updates and see JOHNB internet issues. Good thread. We have two switches near door. One outside light and one ceiling near door. These fixtures need to be ON for the wall switch to activate. I don't see exact model for you but surely someone else with a '93 15' will respond soon. Maybe check brochures here to get model? Be well! Terry