There’s a yellow signal wire to the blower controller at a junction above the brake booster. Set the ACC to defrost and check voltage at the yellow wire. Check voltage at the bigger wires as well. One should be constant 12V the other is ground. The yellow wire sends 0-7V or something like that to the blower controller under the blower. It should register 7V or so on defrost.

Sixto
98 E320s sedan and wagon