Bizarre light behavior - Fiberglass RV

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Old 09-05-2011, 07:58 AM   #1
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skryabin's Avatar
Name: Alexandre
Trailer: Boler 1300 1976
Posts: 17
Bizarre light behavior


I have a 1976 Boler 1300, and I'm working on replacing the incandescent light bulbs with LEDs. Yesterday, while plugged to my vehicle's 12V via the 7-way cable (I don't have a battery for my Boler yet), I tried a LED BA15s in the left rear socket, and it worked perfectly. The right rear socket still had an incandescent light, which also worked (but dimmer). The two interior lights also worked, as well as the porch light (all incandescent).

A few of my side marker lights were defective, so I decided to change the four GE 55 bulbs with new 12V BA9s bulbs while I wait for LED bulbs to arrive. After installing them, the tail lights don't work anymore, nor do the red side marker lights (the ones closer to the rear end of the Boler). And I've noticed some weird behavior... When I put in 12V LED lights in the interior of the Boler (two), when I switch them on the porch light dims... And vice-versa.

Another thing. My yellow side marker lights only work when I switch my towing vehicles lights off. If I switch them on, nothing in my Boler works anymore on the 12V (even the porch light).

Now I realize that the GE 55 bulbs are 6V bulbs. Is that the way to go on a 12V circuit???

I was wondering if anybody has had anything like this happen....



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Old 09-05-2011, 10:14 AM   #2
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Trailer: Trillium
Posts: 712
first of all, the 6 volt bulbs will not last long on the 12 volt system, go back and get 12 volt bulbs.
A lot of the stuff you're describing sounds like bad grounds, check all your connections.

some of the led lights may have blocking diodes and voltage regulators built in too them, which could explain the dimming porch lights.

Check your wiring harness for the side marker lights, make sure that your tow vehicle is wired right then work your way back through the trailer.

Buy a cheap tester for your trailer wiring, they make them for both the 4 way and 7 way plugs, then you know the tow vehicle is right, a cheaper (30-40$) multi-meter would help with the rest.


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Old 09-06-2011, 02:17 AM   #3
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Name: Roger
Trailer: 2009 Trillium 1300 "Homelet"/2014 Subaru Outback "Rosie"
Posts: 2,155
Cool Electrical mysteries

Welcome to the wonderful world of electricity!

The problem with electricity, is it all goes together so wonderfully and then BLOWS UP when you turn it on.

It could be defective grounds. Some strange things can happen with dual filament bulbs, if a fixture is not grounded properly. The current can go through the first filament, to the bulb ground, back through the second filament, travel along the wire for that filament to the next fixture, go through that fixture's filament and then to ground. This would cause dimming of the lights because the voltage is dropped three times, once for each filament. I actually helped a guy that had this problem with the front parking/turn signal lights on his '59 Ford.

I don't know how quirky things can happen with single filament bulbs...

My question would be: Why were there 6v bulbs in the trailer in the first place? Did a FO tow with a 6v vehicle? Are some lights wired in series instead of parallel?

One of the reasons auto manufacturers changed from 6v to 12v is that 12v requires less copper in the wiring? Wiring is sized by the amperage load and 12v will put the same power through a wire with 1/2 the amperage.
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Old 09-06-2011, 03:42 PM   #4
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Name: Rick
Trailer: former Boler, now 1980 Trillium 4500
British Columbia
Posts: 366

Originally Posted by skryabin View Post

I was wondering if anybody has had anything like this happen....


I had some strange behaviour when I installed my exterior LED lights. I eventually found that grounding was the problem. With my battery disconnected, there were separate wires running from the 7 pin connector to the battery, then from the battery to inside the trailer. When I took the battery out, I forgot to connect those wires together, meaning that the ground had to find another route, or not work at all. Check your grounding.

However, the interior and exterior 12V lighting systems on your trailer probably were not wired together anyway at the factory. I assume that you have a place for a battery, but just don’t have a battery at the moment. Those systems, when installed on most trailers, are completely independent and not connected together at all. However, if your trailer never had a battery, then the interior lights would be run from your car battery. There is no reason why this would be a problem, other than only working when the car is hooked up.

The dimming problem sounds like a lack of sufficient current. I would look at your grounding, as suggested by another poster. It could also be a light socket with corrosion where the current jumps from one terminal to another. Your descriptions of the lights (BA9, BA15) describes the socket bases rather than the light bulb number, so it is hard to tell which lights you are using.

If all else fails, start over. Take all the light bulbs out, check the wiring (and grounding) and then install them one by one until you find the problem. There are not that many separate electrical circuits in a trailer so it may be easier to begin again rather than trying to remember where it all went crazy.

Good luck, hope that helps.

Rick G
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Old 09-11-2011, 04:09 PM   #5
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Name: Alexandre
Trailer: Boler 1300 1976
Posts: 17
Hi everyone,

Thanks for all your help. I finally ended up going to the local RV shop, and it was simply my 7-way connector (trailer side) that was completely corroded and two wires were disconnected. Bizarre how this suddenly happened, or maybe my wires were really really close to disconnecting. Anyhow, we're talking about a '76 Boler... So no wonder all my tests were not giving anything sensible. Got myself a brand new connector, and voilà, everything works as it's supposed to!

Have a great one,

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