the 90 model 420sel had a 2 prong blue temp sensor and it was wired [thru relays]so that if the sensor went bad OR the plug was off the fans would run all the time on high speed.seems that on your car this sensor was left out of the swap.

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David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
http://www.w108.org/gallery/albums/A...1159.thumb.jpg