[Elecraft] Another odd behavior

[Stuart Rohre]

The LED is simply a diode that glows.  It is entirely possible this LED has 
enough response at RF frequencies, that it is responding to your RF keying 
waveform, as well as glowing with the steady DC of the supply.  You might 
try a clamp on ferrite choke between the Rig Runner and the rig.  You may 
have to slide it along the cable to find the point of optimum suppression. 
At that point, use cable ties to position the permanent installation of the 
clamp on choke.

Stuart
K5KVH