View Full Version : Shorted Running/Clearance Lights

Ron and Susan
07-12-2010, 03:17 AM
I just installed rear and side cameras (thanks to Tom for pictures and assistance) and decided to check all electrical circuits.

I found that the 20 amp fuse for the running lights was blown. The last time I checked the running lights was almost a year ago.

I measured about 0.2 ohms to ground for the circuit and then removed the large gausge white wire that disappeared behind the fuse panel and found that the wiring from the fuse through the running light switch and back to the terminal block (located under dash on passenger right side was not shorted). Only the large gauge wire going behind fuse panel was shorted.

I removed several of the running lights and found no physical problom. However I did measure about 1.2 ohms from the 12 volt terminal of the lamp to the external skin where most lamps are connected for a ground.
12 volts at about 1.2 ohms would be about 10 amps and does not indicate a short.

I suspect the short is behind the fuse panel or where the wire passes through a bulkhead.

Does any one have nay thoughts ??

Frustrated electronics engineer
Ron Gookin

07-12-2010, 07:40 PM
Hi Ron,

I have just recently been through a similar exercise on my '99. The valence light circuit blew fuses when I got the coach. In fact I later learned the circuit had never worked even for the previous owner. I did the easy stuff first like disconnecting all the know loads on the circuit and making sure all the known switches were open. Even then there was still a short to ground. At that point I installed a 12 volt light ( actually used a rope light so I could see it anywhere in the coach as I was working alone ) in place of the fuse. As long as the short was still there the light would be on. Then I proceeded to wiggle all the wires in the paths I could find between the fuse panel and the load. No joy, light stayed on solid all the time so I had to conclude the short was very solid. Next I obtained a great troubleshooting tool which is a small clampon DC ampprobe that plugs into my Fluke DVM. I had about 4 amps flowing through the short and my rope light. Now I started following the actual wire as I could identify it by the current flowing.
Sometimes beauty is only skin deep in a Newell. If you look at the attached picture you will see why. As I followed along the wire chase above the stove I pulled on the wire and watched to see which wire moved in the wire chase above the sink. What! I pulled on a red and a blue moved. Impossible, they must be tied together with wire ties, but I could find no red wire. Finally I moved the current probe to the sink chase and the 4 amps was now in the blue wire. What could be going on? So, to find out, I removed yet another wiring cover and you see the result. They ran out of red wire and just butt spliced onto a blue wire and kept going. I don't know what you think about that, but anyone that would have pulled a stunt like that in my industry and got caught would be out of a job. Now things started to fall into place. I had seen a similar blue wire on the valence switch in the step well. The short existed in the side wall of the coach somewhere between where the wire went into the wall over the sink and where it arrived at the switch in the step well. There was lots of foam insulation around the wires and no way to get closer to the fault. I solved the problem by isolating the faulted wire and connecting the valence circuit to another lightning source with sufficient capacity that was available in the step well area. Isolated wiring was tagged on both ends with a label explaining what had happened. Fuse circuit labels were updated. I now have my valence lights all working. It took the better part of a day and I will think of that day every time I turn them on. Hope some of this helps. Russ