W124 ambient temp sensor removal

[AlexTheSeal]

The ambient temperature display in my 300D isn't working, and I think I've narrowed it down to the sensor. I have a replacement thermistor, and looking at the CD manual it should be simple to get at the old one, clip the wires, and solder on the new one.

But what I see when I take off the license plate is different from the picture on the CD. There's a round grommet behind the plate that is supposed to cover up the thermistor. The picture makes it look like the wires come out from the lower edge of the bumper, then run sideways for a couple of inches to the grommet. But on my car there are no visible wires, and behind the grommet is what appears to be a block of styrofoam or something similar.

Is this normal?
If it's not normal, was my car perhaps front-ended and repaired badly?
Should I take off the bumper to see what's going on? Any tips for removing the front bumper, or getting access to the space directly behind it some other way?

Thanks!