What the hell is the "Emission Switch Maintenance Warning LamP"

I had an issue with my speedo last night on the way to a cruise. The speedo neelde was going crazy then got stuck maxed out and would bounce occasionally. I removed the cluster today what a ***** that was, but under the hood the cable is in 2 parts and in between is some sort of cutting edge 70's technology. cable goes in one end comes out the other and has a wire connected to it. Part Number is 3747025. It is a 75 dart with a 318. Can i eliminate this thing or is it necessary for the car to work. Now i also need to find the issue with the speedo.

Yes you can do away the piece inline on the speedo cable, it's a mileage counter for the EGR system and sets off the emissions maintenance light every 15000 miles. You'll need to replace the speedo cable with the one piece style.

I can still remember some of us gagging and puking when we looked under the hood of progressively newer '70's vehicles.

I used to call the "absorbent" bumpers "picnic tables." Seems like Ferd/GM had some of the worst