If there is no power coming into strip fuse , then the suspect is the Ign switch. Put a Test lamp on the fuse in-line and jiggle the ign sw a few times .

Aux fan still has nothing to do with Blower circuit, so forget about that..you just happened to have a blown 15 A fuse for low AUX fan b/c that fuse has been upgraded to a 25A by Benz and they all blow w/15A... aux fan is a completely different system..you have just been driving around with no aux low fan for a/c operation w/o knowing it.... That's all. That fan relay is triggered by a pressure sw that keeps the a/c systems high-side pressure inside the condenser in check by adding aux air across the condenser. That is ALL it does and is ALL it is there for. And it NEVER comes on w/o a/c being on.
SO,....Another simple test w/o getting to blower and regulator is to bring a jumper wire over to the strip fuse from the battery Pos + terminal..that eliminates the possibility of bad ign sw. Then try blower on Defrost CP position.
If you have no power at yellow , then suspect is Ign sw or CP.


Give those findings ..

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A Dalton