I have a '90 w124 2.5L turbo but my comment is universal.

I have a medical condition called multiple chemical sensitivity/environmental illness. It's a mouthful. It's now much better but 10 years ago it crippled me. The smallest amount of dust, solvent or combustion product and my body would go into shock.

I'm obviously grateful to be doing much better. However, diesel fumes still bother me. I have done a very simple mod to keep the fresh-air inlet at a constant 80% recirc setting. It is a big improvement.

I would now like to make a modification to my original mod and that is to only have the vehicle in the recirc mode while stopped or in stop-and-go traffic. If I can find an electrical signal that will indicate that the car is stopped I will use that to drive a circuit which will then energize the recirc pod.

Ideally this will let the car draw fresh air while driving on the highway but close it while in congestion. The brake signal wont work and I have thought of somehow taking the signal from the tach and using that. But I am a chemical/material science guy and my knowledge of electronics is limited.

What would be ideal would be a signal that would shift to one state while stationary or traveling less than 10 to 20 mph and then shift to another state at higher speeds.

Thanks.