How to further pinpoint lighting circuit short

[cwalt84]

2011 Bighorn 5th wheel - Converter went bad, at the converter on the DC side, with the leads off, I have continuity between positive and negative until I pull the fuse for Living Room Lights.

Are wiring schematics available online anywhere? I've failed to find any so far.

How should I continue my search for the short, where is the most likely location? There's evidence of mice in the ceiling during winter storage but considering the wiring chase is styrofoam - not likely a hot touching the frame but maybe a positive and negative touching so how would I test these conductors in a chase I cant access, or should I be looking elsewhere to start?

Thanks for any advice 🙂

[BB_TX]

A cold incandescent light bulb is basically a very low resistance wire when measured with a meter. When power is applied that wire (filament) heats rapidly and the resistance also rapidly increases. Much higher resistance than before power is applied.

[cwalt84]

CA Traveler wrote:

cwalt84 wrote:
Had an electrician help me trouble shoot originally and hes the one who said to leave that fuse out until I find the short.

It pains me to say this but there can be a vast difference between an "electrician" and someone skilled with RVs like Doug above.

Intermittent problems can be difficult to find. Put the fuse in and drive. Or remove every thing on the circuit and wiggle the wires etc.

Will do, thanks to you both 🙂

[CA_Traveler]

cwalt84 wrote:
Had an electrician help me trouble shoot originally and hes the one who said to leave that fuse out until I find the short.

It pains me to say this but there can be a vast difference between an "electrician" and someone skilled with RVs like Doug above.

Intermittent problems can be difficult to find. Put the fuse in and drive. Or remove every thing on the circuit and wiggle the wires etc.

[CA_Traveler]

cwalt84 wrote:
My guess on the converter going bad is someone yanked the breakaway cable and brakes were activated for months. Not sure if that constant drain would cause that? A constant drain should not cause a converter problem. But replaced the breakaway switch and pulled the living room lighting fuse, replaced converter and all has been good for a month now. Always plugged into shore power.

I had no blown or bad fuses anywhere.

Ya Im talking about the leads between the converter and the fuse box, when disconnected from the converter, have continuity until I pull the Living room fuse. No power to the RV and battery disconnected during that continuity test. Every RV has loads that cannot be switched off like smoke detectors, etc.

Sounds like I should disconnect all the lights on that circuit next and test again. Thanks for the help. Ill test by removing the leads at the converter so nothing on the circuit can possibly be ON, completing the circuit.

[cwalt84]

CA Traveler wrote:
Continuity may not be meaningful since a single bulb etc could have low resistance. Have you connected 12V to the circuit and a fuse blew?

If you actually have a short what fuse blew? Add a light bulb in series to that circuit and it will be full brigntness with a short. Then as you open downstream wiring and when the light turns off you can isoate the problem and resolve as needed.

And a wire tracer can be very useful in determine wire routing.

No fuse blew but I thought on a circuit of only lights, with no power, continuity would only be present between + and - if the positive is touching ground or touching the grounded negative.

I did just put the fuse back in and lights work, except one, Im just unsure if I should keep that circuit powered since I believe theres an issue in that circuit.

Had an electrician help me trouble shoot originally and hes the one who said to leave that fuse out until I find the short.

[cwalt84]

dougrainer wrote:
The Converter did not go bad because of the Living room light short. The Living room light circuit is protected by that fuse you pull. DO YOU HAVE ANY FUSES BLOWN/BAD? To answer your question. The way you trace down a short for one circuit, you disconnect EACH appliance/light on that fused circuit. Then see if the short goes away. That determines if you have a appliance short or a short in the wiring(mice possible). Now, if you have a light ON(or any appliance in that circuit ON) and you attempt to get continuity and GET continuity. That just means the circuit is complete, NOT that you have a short. When you state LEADS OFF. Are you talking about the Pos and NEG leads that connect to the Power Converter? Doug

My guess on the converter going bad is someone yanked the breakaway cable and brakes were activated for months. Not sure if that constant drain would cause that? But replaced the breakaway switch and pulled the living room lighting fuse, replaced converter and all has been good for a month now. Always plugged into shore power.

I had no blown or bad fuses anywhere.

Ya Im talking about the leads between the converter and the fuse box, when disconnected from the converter, have continuity until I pull the Living room fuse. No power to the RV and battery disconnected during that continuity test.

Sounds like I should disconnect all the lights on that circuit next and test again. Thanks for the help. Ill test by removing the leads at the converter so nothing on the circuit can possibly be ON, completing the circuit.

[CA_Traveler]

Continuity may not be meaningful since a single bulb etc could have low resistance. Have you connected 12V to the circuit and a fuse blew?

If you actually have a short what fuse blew? Add a light bulb in series to that circuit and it will be full brigntness with a short. Then as you open downstream wiring and when the light turns off you can isoate the problem and resolve as needed.

And a wire tracer can be very useful in determine wire routing.

[dougrainer]

The Converter did not go bad because of the Living room light short. The Living room light circuit is protected by that fuse you pull. DO YOU HAVE ANY FUSES BLOWN/BAD? To answer your question. The way you trace down a short for one circuit, you disconnect EACH appliance/light on that fused circuit. Then see if the short goes away. That determines if you have a appliance short oor a short in the wiring(mice possible). Now, if you have a light ON(or any appliance in that circuit ON) and you attempt to get continuity and GET continuity. That just means the circuit is complete, NOT that you have a short. When you state LEADS OFF. Are you talking about the Pos and NEG leads that connect to the Power Converter? Doug