Mystery black box behind battery in 300E
 

Yesterday, I was rooting around the engine compartment to look for the resistor that retards the ignition by 6 degrees (found it eventually) but in the process found a box that I have no idea what is for. It is behind the cheezy black cover behind the battery. It is a black box that looks kinda like the DME unit, but has a knob on the top of it that can be selected to position "0" or "1". Right now it is on "1". What is this box? Thanks -- Mikey

Apparently you have a 90 or later production car with a MAS relay. The knob "locks" the relay to the connector.




Joe

what's a MAS relay and why the differant positions (0,1)?

MAS is the combination relay that handles the heavy current users of the engine: fuel pump, A/C clutch, air pump clutch maybe others.

The two positions are connected and disconnected. The thing is so big that I guess MB decided there needed to be a lock to keep the thing engaged. If you turn the knob, the relay will rise from its position and disengage itself. It screws itself back in also (if you have everything lined up).

Black box
 

Hello!
My car is a W124 300TD turbo from sep. 1990 and in the compartiment behind
the battery there is a "black box" to. The manual mentions it as the "brains"
of the ABS brake system. They talk about it because it is important to take it out or deconnect when doing electric welding on the body: it wan't survive
and it is certainly VERY pricely!
Danny M.

The ABS Control unit (ECU) is also behind the battery, but usually has a very large multi-pin connector along the top, and no 1/0 switch.
I've never seen one of these MAS relay boxes before though, and would've been pretty confused by it!

later