OK, against my principles
I read those s@%tty charts and, bottom line, you can't!
The MB sensors trigger around at (200-300 ohms) low ohms and it appears from what you said, the Derale triggers at 3.xKohms, high ohms.
You CAN'T add a series resistor that's an order of magnitude greater than the desired trigger point, since that resistor will swamp the resistance trigger point.
Now if you want to build an 'amp' whose trigger point is, say 93 ohms that in turns kicks in a relay that will turn on the fans, that can be done. But it's a start-from-scratch-circuit unless we can find something from Radio Shack (as an example) that can be modified to do what you want using the MB sensor.
It can be done but not with what you currently have!
Regards . . . . JimF
'94 S500 Cpe
Visit my Mercedes Web Page
Last edited by JimF; 09-05-2002 at 02:07 AM.