Actually you *may* have a problem now, w/1/4" jacks.
The number of leds lit depends on 2 factors, choosen level impedance and how send to Eclipse level is set.
With a +4dB device you must use XLRs on Eventides. The fact you don't see yellow led lit may definitely depend on how high is the playing level on your amp. Most amps use the Master output as FX Loop SEND level; this is a bit awkward as the connected processor can only be properly driven by a hefty master out setting, that is the amp has to be played quite loud to run the FX as it should. Other factors may be in charge here but having no other info there's not much speculation to do.
As I suggested, try XLRs and raise the amp pot that controls FX Loop send (check the amp manual) until you see yellow led going on.
Some amps have a dedicated SEND pot close to the FX loop (good!)….
all the best