The fuel pump relay behind the battery on my 88' 300E has a small black plastic knob (smaller than a dime) on the top corner of the relay. What is the function of this small knob? It is broken off on mine but does not appear to have any effect, but I want to make sure it is not a problem.

This is the inter-locking, speed sensing, super power button.

JUST KIDDING....It is a vent. They have gone away from this type on the newer ones. The only thing that could happen would be moisture in the relay. This is not very likely.