[Elecraft] Wiring 101 question

[Tim]

Hi folks -
  The nice thing about this reflector is that nobody calls you an idiot when
you ask REALLY simple questions - at least so far hi hi!
  So here is the simple question. I just made a second power cord for my
K2/100 so that I could locate the antenna tuner on a different shelf rather
than right under the K2/100.
  Both the old and new cord have a "Y" joint which takes power from the main
lcord and runs it to the ATU. The second power cord has a much longer ATU
line though. It's about 6 feet long. There is a "Y" joint about 2 feet from
the radio end of the cable and the fuse is about a foot from the opposite
end. The ATU cord length is about 2 feet. Before plugging this new cable in
I checked the voltage at the radio and and on the ATU jack end - all was
fine. Also tested for any shorts - all was fine. The problem is that when I
turn on the rig with this power cord I get a loud noisey, steady hum - which
made me turn the rig off immediately. It occurs regardless of whether the
ATU section is plugged into the ATU. When I put the original power cable
back on and no problem.
  I'm just a solder jockey that could not troubleshoot his way out of a
paper bag - but the cable delivers proper voltage and has no shorts - fuse
is OK - what could I have done wrong? How can I determine the cause of this
kind of issue? Thanks for any help folks!
73/Tim NZ7C