trailer electrical systems

Kent Crispin (kent@songbird.com)
Sat, 20 Mar 1999 06:26:46 -0800


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West Wight Potter Website at URL
http://www.lesbois.com/wwpotter/
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Here I was, driving down university avenue in Palo Alto, on my way to a
Very Important Meeting, crawling from light to light at sailboat
speeds. It was OK, though, because I was still early, and had plenty
of time. A car pulled up on the right side; the driver frantically
motions to me to roll down my window. Fortunately, I have a modern,
well-equipped vehicle, and I only have to touch a button to comply,
instead of leaning way across the passenger seat to turn a crank...

The driver yells "You're on fire!".

"Thanks!", I yelled. I looked back -- no smoke, no flame. Probably a
damned crank, I thought, but I better check it out.

Of course, traffic was stop and go; every parking space was taken;
and halting traffic was unthinkable. I made a right turn onto a side
street -- still no good place to stop. Aha -- a fire hydrant red
zone. It was an emergency. I pulled off, left the motor running in
case I had to make a quick getaway, and hopped out of the car.

But indeed, there was a fire: the dangling plug that joins the
vehicle electric system with the trailer lights was slowly melting
into a smoldering smokey mass of black plastic. I ran to the front
to turned off the engine -- it was obviously an electrical fire
caused by some kind of short in the plug.

Because time was short, I simply clipped the wires, and removed the
plug. I later discovered that the taillight fuse was blown, as
well.

It turns out that the plug is actually a great deal more complicated
than it appears -- the wiring of most trailers is not directly
compatible with the wiring of the taillights on my vehicle (a Toyota
4-runner), and that plug includes converter circuits with diodes that
allow the connection. Though it's never supposed to happen,
sometimes those diodes do go bad, and when they do there can be a
direct short in the plug.

Just one of those things that I never knew you needed to know...

-- 
Kent Crispin                               "Do good, and you'll be
kent@songbird.com                           lonesome." -- Mark Twain