I fixed the radio antenna in my car today, so am posting the wiring colors and operation for posterity. I found conflicting info in other posts, some due to year differences and some maybe errors. My car is a 1985 CA model, W123 300D. Earlier models (pre-1984?) had a 3-wire antenna that is simpler. My antenna has 5-pins. My Haynes manual has a 1984 wiring diagram but shows a 3-pin antenna.

Antenna pins:
1 - blu/yell from up/dwn switch (max)
2 - red & red/wht, +12V supply, 1 wire passes thru to trunk lamp switch
3 - not used
4 - blu/grn, outputs +12V when radio on
5 - blu/wht from up/dwn switch (mid)
6 - brn, to chassis ground

Up/Down Switch on dash:
1 - empty, jumpered to 2 on switch
2 - blu/wht
3 - blu/grn, "radio on" signal
4 - blu/yell
Swith in down position: no connection between any pins
Switch in mid position: pin 3 connects to pin 2
Switch in up (max) position: pin 3 connects to pins 2 & 4

Radio:
brn - gnd
blk - 12 V power, same as cigarette lighter
red - ?
vio - ?
blu/grn - separate spade connector, +12 V when radio is on

It appears there is a junction somewhere in the PVC sheath that splits the blu/grn "radio on" wire to both the up/dwn switch and antenna. I see just blk PVC tubing on mine at the up/dn switch but others said "blue wire" when stripped back. It ohms out as being the same wire.

This is how I infer the 5-pin antenna control logic works:
pin 4 off: antenna goes full down, regardless of other pins
pin 4 on, pins 1 & 5 off: antenna goes full down
pin 4 & 5 on, pin 1 off: antenna goes to mid position
pin 4, 5, & 1 on: antenna goes to max position

I don't know if pin 1 on is sufficient to go to max position, regardless of pin 5, but expect both must be on.

I expect one can "program" the mid position to be anywhere desired by flipping the switch from "max" to "mid" at the desired position. The antenna will then return to that position each time you start the car, if you leave at the "mid" setting. If so, it could be an electro-mechanical design inside the antenna. My only owner's manual is 400 miles away in my son's 300D.

In my case, the antenna problem was simply that the "radio on" spade connector was unplugged. I am getting the car back on the road after sitting in the garage 3 yrs awaiting an engine and don't recall everything, but I have been borrowing parts for my son's car.

Well done. Trouble shooting an antenna has always been confusing.

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Peach Parts W124.128 User Group.

80 280SL
85 300SD
87 300TD
92 300D 2.5 Turbo
92 300TE 4Matic

A few years late to this post but looking for info on how to wire a universal power antenna with 3 wires. I wanted to reuse the male end of the old antenna. I’m thinking there needs to be a loop somewhere with the yellow/green?

Cheers. Russell

I wrote a how-to for a W123 that may help you.

Hirschmann Universal Antenna in W123

Dkr.