i/o switch
 

What is the little i/o dial type switch next to the computer in my 1991 300e?? whats its purpose..

Sounds like you are refering to the retaining device on a MAS or DM.

As the size of these boxes went from small relay to approaching the size of major controllers, MB evidently got worried about the ability to retain a good solid connection.

The relay is p[laced just so in the socket and then it is pulled the appropriate distance into the connector by the semi rotating screw knob on the top. The two positions I and O are in and out (maybe not in that order) couterclockwise is Out and clockwise is In. To remove the relay just turn the knob.

The MAS is a replacement for the OVP, fuel pump relay and the klima relay. Everything was consolidated when they started needing more such relays. The MAS also does at least the power circuit for the secondary air pump (clutch coil in your case).

not that im going to but what would happen if i switched the position?

The relay would then be in your hands not the connectors (unplugged).

well i understand that it would then be in my hands,, what im trying to figure out is what do? does it affect hoe the car runs?

Car won't run.

Peter

I don't understand your question. if you understand that it is in your hand and you read that it does the job of the oVP and the fuel pump relay then it should be obvious that the car won't run with it out.

With it out nothing that it runs will work. With it in it works unless it is broke. What else would you like it to do?

I understand what you mean now, i misunderstood you i apologize..