But that's just because you set the top layer to normal blending and set it to essentially be a "black" emitter. Since it's set to normal blending, anything underneath this layer won't be visible, unless you start lowering the layers opacity/weight.
You CAN put both the emitter component and two BSDFs in one layer (as numerobis asked), to have a plastic like material that doesn't use any additive layers. When you turn off or lower the intensity using Multilight, it will start to reveal the two BSDFs. But in AlexP case, he still wanted to use Additive layers and in that case you should put the emitter component either in this additive layer, or on its own in a third layer, also set to additive.
EDIT:
This part: "
Or add the emitter with a new layer but using normal blending and not additive." will of course turn the material black when you turn the emitter off, like Brian showed.
But this part:
"I would just take two BSDFs + emitter in one layer" will reveal the BSDFs when the emitter is off as the screenshots above show.
Again, plastics tend to look better using Additive mode, and in V3 you no longer have to worry about using too many additive layers, which in itself is an extremely important fix.
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