My 35 year old Hirschman antenna finally died so I replaced it with a Universal Hirschmann. It cost less than $100. I did some research and couldn't find anyone documenting the install for a W123, so I figured I would write up my install notes.

To start, remove the old antenna and pull the conductor cables out of the plastic button connector assembly. Use a multimeter to check each conductor with the engine off. One should produce 12.x volts coming directly from the battery. Then turn the radio on and check the conductors again. One should produce 12.x volts with the radio on. The other conductors can be taped up and tied up together.

The red wire connects to the conductor with battery voltage and the green wire connects to the conductor with radio-only voltage.

The universal kit comes with a number of connections that I found to be completely unusable. I wanted to re-use the antenna grommet so it was more servicable in the future.

I threw out everything except for the spacer shown on the left hand side of the picture and the nut on the right hand side and was able to keep the OEM grommet. If yours is ancient, it probably will not survive being removed and you may want to keep it.

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