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Old 05-15-2007, 11:11 AM   #1
FT RVing
lebolewis's Avatar
1976 31' Sovereign
Always searching for a place w/low Humidity , FT RVing, N & S, E & W, & in between
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Posts: 271
The Dreaded Electrical Short!!

After almost a year of repairs and replacements..... Friday, I headed out on my "shakedown" trip. All hooked up and ready to go......oops, something is amiss...no tail lights or running lights!! Crap, now what! They all worked the last time I towed. Some simple checking did not reveal the problem. I had all other lights, stop, turn, back-up and brakes on the trailer, just no tail lights or running lights! NONE! Now what to do?

Since I would not be traveling at night, I just went anyway, and since I did have braking on the trailer, stop lights and turn signals, I figured I would be OK.

Returned home two days later and everything else in the AS worked just great!.....including the 30 year old Armstrong AC...it purred along just fine and put out very cold air. But still no tail lights and running lights. Hmmm.

Initally, I thought the problem was in the Suburban. But I checked all the connections and voltages at the connector and all seemed "normal", except the pin for the tail lights and running lights was a bit LOW, only 11.5 volts, should be at least 12.5 volts. Hmmm....MAYBE no big deal.....MAYBE. So, I then I concluded it was likely an "open" or "shorted" circuit in the trailer somewhere. The thought of the DREADED possibility of a shorted wire to the trailer frame somewhere inside the walls came over me......and I shuddered . But, if it was shorted, it should have blown a fuse or breaker somewhere! Checked everything...no blown fuses....Then, I noticed from the wiring diagram, that there was a 15 amp auto resetting circuit breaker in this line just behind where the connector plug enters the trailer frame. I looked and the box where the breakers were was "impossible" to get to without removing the Goucho. Ugh, what a design flaw! I then measured the resistance from the trailer tail light/running lights pin in the trailer connector to ground and it was about 1 or 2 ohms. Well, at least there was continuity through the breaker, and not ever having measured the resistance to ground on that pin when it was working, I figured that could be about normal, considering all those bulb filiments were in parallel to ground and that breaker seemed OK........or it may be SHORTED to ground on the other side of the breaker!!!! 1 or 2 ohms is close to a SHORT, considering that the wire itself has some resistance! UGH!!

OK, not to be defeated, I'll try one more thing and maybe that will give me a further clue. I kept my old 12.5 volt trailer battery (such a good idea!), so I used it to apply 12.5 volts to the the circuit on the back side of the breaker by removing the lens from one of the side running lights. I decided to fuse the connection with a 15 amp, in line fuse, to my battery terminal and when I applied the voltage, the lights lit, hooray.......for about 5 seconds and then out! It blew my fuse to the battery. Hmmm. Maybe I'll try a 25 amp fuse. 10 seconds the lights were on and then it blew the 25 amp fuse.......definitely the DREADED SHORT!!! RATS!!

I decided to check the easy stuff first. I started with the running lights on the front and found most of them to be in bad shape. The heat from the sun and 30 years age have caused the plastic in them to decay and crumble and the metal parts holding the bulbs are no longer secure and making good contact with the bulbs. On the 6th running light I checked......there it was.....the DREADED SHORT!! (See photos). One of the bulbs had popped out and the pressure from the other bulb had forced the 12 volt terminal over to the left, touching the grounded part of the socket.....ZHAZAM!!....SHORTED TO GROUND!!

I will be replacing 7 of my 10 running lights. I found them at a cheap price on the Internet ($2.38). Email me for source at lebo@isp.com.

The moral of this story is.....that it is appropriate to fear the DREADED ELECTRICAL SHORT, especially if is somewhere deep in the bowels of the trailer, almost impossible to find and almost imposible to get at to repair!! But, check the easy stuff first.....it may not be so bad!!

Cheers, Bill
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Old 05-15-2007, 12:18 PM   #2
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2006 25' Safari FB SE
St. Cloud , Minnesota
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Good detective story.

I changed a marker light bulb once when attached to the umbilical with the lights on -- and blew a fuse under the hood in my tow vehicle. Knocked out all my running lights. ('74 Argosy & Nissan Titan)

Always check for loose connections if the umbilical plug is a replacement. All sorts of simple causes. Look for sparrows not canaries, grasshopper.

5 meter Langford Nahanni

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Old 05-15-2007, 03:16 PM   #3
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1993 25' Excella
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Electrical shorts are not fun. But are easier to hunt down when using the "half splitting" method like many electricans do. My husband is a Master Electrican and he just did an electrical supplies and troubleshooting seminar at the New England Unit's May Maintenance Rally. Here's the training document he did up - on page three you will see how he used the half splitting method to solve the electrical short in our Airstream.
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Michelle & Leon
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Old 05-15-2007, 03:49 PM   #4
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1976 31' Sovereign
Always searching for a place w/low Humidity , FT RVing, N & S, E & W, & in between
Join Date: Apr 2006
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Originally Posted by myboyburt
Here's the training document he did up - on page three you will see how he used the half splitting method to solve the electrical short in our Airstream.
Thank you for the Trobleshooting Document. It looks like interesting reading. Sometimes these electrical problems can be very difficult to diagnose....and you need all the help you can get.

I thought of another question for any 70's Sovereign owners that might read this. In my forward overhead storage compartment above the Goucho, there is a fairly large, almost clear, stiff plastic conduit that comes in from the left side through a hole in the wall with a grommet. It runs over a little past half way across the compartment. No doubt, it was put there by Airstream. This conduit has just one wire in it. The wire is fairly heavy bare solid copper and is inside a mesh metal shield. Since the wire is bare, the purpose for the shield escapes me. I cannot figure what this thing was for! I've scanned the wiring diagrams and they give no clue. Anyone know what this is and what it was for? Thank you, Bill
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