I like the idea of using the factory switch as a low-key add on. Great idea!

On my 123, I installed a *really* simple home-brew setup that can be made with a small one-way brass valve with a simple ball & spring inside. I got it from Graingers, but it's been many years ago so my memory is fuzzy.

It delays the boost pressure signal from reaching the wastegate until boost has built up enough to overcome the valve's pressure setting. That allows the wastegate to stay seated longer before opening, as they have a tendency to open a bit and bleed off before full boost is achieved. If you combine the "new" valve AND adjust your wastegate to factory specs, you get a much nicer throttle (?) response. There would be no need to switch between the two functions, as you would not exceed the factory boost specs. (if that's what you set your wastegate at.)

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Current rolling stock:
2001 E55 183,000+ Newest member of the fleet.
2002 E320 83,000 - The "cream-puff"!
1992 500E 217,000+
1995 E300D 412,000+
1998 E300D 155,000+
2001 E320 227,000+
2001 E320 Wagon, 177,000+

Prior MBZ’s:
1952 220 Cab A
1966 300SE
1971 280SE
1973 350SLC (euro)
1980 450SLC
1980 450SLC (#2)
1978 450SLC 5.0
1984 300D ~243,000 & fondly remembered
1993 500E - sorely missed.
1975 VW Scirocco w/ slightly de-tuned Super-Vee engine - Sold after 30+ years.