Date registered: Jun 2012
Vehicle: 1998 E320 base sedan @ 160kmiles
Location: Boca Raton, FL
Mentioned: 79 Post(s)
Quoted: 1191 Post(s)
If you are into electronics, you should be able to get a curve for the coolant temp sensor for the A/F, and plot the resistance value at 100 degrees C (first stage), then plot the resistance value for the 75 degrees C the temp that you want the fans to start. Then calculate the resistance value you need in parallel, to give you the effective resistance value at 75 degrees C.
1/R75 = 1/R100 + 1/Rx
1/Rx = 1/R75 - 1/R100
1/Rx = (R100 - R75) / R75 * R100
Rx = R75 * R100 / (R75 - R100)
Assuming a linear relationship : If R75 is 400 and R100 is 300, Rx is 1,200 Ohms.
If you claim your A/F starts turning at 80, then you need R80 value in the graph, instead of R100 on the curve.
Then again, I believe you are barking the wrong tree.