1980 450 sel throttle valve switch
 

I recently got a 1980 450 Sel that has no throttle valve switch on it, so I've never seen where it hooks up to. I know where the switch connects to the throttle valve body, but not the other end of it. the only place on the firewall that has a hole with nothing in it (there's a small hole with a rubber grommet directly behind the engine a little to the passenger side from the center of the firewall) looks to be too small for the three pronged plug end of the cable to go through it. I thought there would be a plug in somewhere on the firewall to connect it, but I can't find it. I'm wondering if there was a cable that ran through to the engine compartment that's broken off. Also I haven't found anywhere to even purchase a throttle valve switch, but I haven't checked a Benz dealer yet. Are these things still available ? Any help will be greatly appreciated, Thanks for your help.......... Rocky