Hey all, I need some help.

I just purchased a 89 300e that needs some fixin. I've been a Saab guy in the past so Mercedes are a different flavor for me.
Here's the deal. I have two large cables with nothing to plug into directly behind the battery on the left as I stand in front of the car. There are two empty brackets that obviously hold some electronic componets that the cables plug into. Problem is those componets are gone. Does anybody have an idea what those componets are? The car does not run due to a dead battery and a head gasket issue and maybe these missing dodads. The cables are grey and resemble old time printer cables Anything that anyone can offer is much appreciated.