Interesting relay failure

From: jon@dakota-truck.net
Date: Thu Sep 02 2004 - 21:28:03 EDT


  This is actually on my '01 Ram, but I guess it could have just as
easily been on a Dak. ;-)

  The fog lights went out on my Ram a few weeks ago, and I have just
recently gotten around to looking to see what the problem might be.
Checked the fuses, and everything was fine, looked into the lights
and the bulb filaments seemed OK, then I got under the truck to
look at the back of the lights and discovered that they were
aftermarket - not factory fog lights! So, I trace the wiring and
find the fuse (not blown), and then the relay. I had disconnected
one of the fog lights to test to see if the truck was feeding power
down to the light (it wasn't). Just to be certain, I fed power to
the light directly and it worked, so now to figure out why power
wasn't getting to the lights. I pulled the relay out and checked
the connector, everything was OK, constant power, the trigger voltage,
ground all OK, and jumpering the switched lines turned on the fog
lights. With the relay out of the connector, I checked for continuity
across the switched terminals with an ohm meter and applied power to
the control terminals. The relay made a nice, healthy click and the
switched terminals connected together. So, at this point, I have
eliminated a faulty connection, except possibly within the relay
connector itself, and I have a "working" relay. I plugged it back
into the connector test the lights, and nothing. With the relay in
the connector, I applied power to the control circuit separately,
while checking the continuity of the switched circuit, and...
nothing. I pulled the relay, then hooked the wiring up to a new
relay, and the fogs work great!

   So, long story short, this relay worked just fine, unless you
actually had 12v on the input pin; I thought that was interesting.
:-) Since I don't have a lot of relay experience, I was just
wondering if anyone knew if that was a normal "failure mode" for
a relay? I would have expected a mechanical relay like this to
either work, or not work, but to see it work only when it wasn't
actually switching voltage was a bit unexpected. :-)

-- 
                                          -Jon-

.-- Jon Steiger ---- jon@dakota-truck.net or jon@jonsteiger.com --. | 1970 Barracuda - 1990 Dakota 'vert - 1992 Ram 4x4 - 1996 Dakota | | 1996 Intruder 1400 - 1996 Kolb FireFly - 2001 Ram QC 3500 CTD | `------------------------------------ http://www.jonsteiger.com --'



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