I also have a few of these and needed to use them in a 4 wire hookup-they do not contain the parts or electronics to work as a 4 wire unit. are 2 wire only. The 4 MOV's inside - two are for the phone line and 2 are for external 12 volts AC the other TWO that WOULD be used in four wire are absent as ...

I am looking for either a service manual or information on the dip switch settings for the unit.
I need these to work as a 4 wire unit instead of the normal 2 wire unit.
Would be nice to know what the dio switch setting do as well.