Engine not stopping after turning off with key
 

Recently replaced the heater fan motor in our 1988 240DL, and in the process of putting everything back together, after successfully turning on the car it doesn't turn off. We have been doing the internal electricity and are wondering if it has something to do with the ignition switch. Everything else seems to be working fine, but the car doesn't turn off when the key is turned off. Is there some other switch or cord that controls the starter?

It is the ignition switch. Replace it-not expensive or hard to do.

Just tried replacing the ignition switch like you said, but still the same problem. The only way it turns off is by disconnecting a green wire inside the dash.

What did you replace in the switch. Was it the electrical part on the back of the switch. That is usually the part that fails.. Was it a new one or used. If new and it didn't fix the problem then your repair caused the problem. That being the case you need to go back and retrace what you did. Get a wiring diagram and start following the circuit in the area that you did the work.