Stationary Heater Control Unit, Component Description - GF83.70-P-4066A

Model 223 

with code 228 (Additional warm water heating) 

Courtesy of MERCEDES-BENZ USA

The numbers on the pins indicate the pin numbering of the slots.

Fig 1: Stationary Heater Control Unit Components Location - Model 223 With Code 228

Courtesy of MERCEDES-BENZ USA

Location