If this is build up like an SL, there will be a 3 wire connector / terminal strip just behind or to drivers right of the power brake booster for the fan controller. There will be 2 large and 1 small wires. Near as I can tell the fan controller ( which sits atop the blower housing) is just a power transistor.

On the R129 SL you can see the controller by pulling the cabin air filter located under the hood.