If your iDrive 300 Manual switch may be giving your some issues and here is a process in testing the switches functionality.
Please view the following video link to show you the process of testing the switch.
iDrive 300 Testing OPEN - CLOSE Manual Switch
with your testing you will have to have one meter lead on the Common
and the other meter lead at 2 different locations, from the Solder points from the switch itself
as well as a point on the J1 Portion of the Printed Circuit Board
When testing you would have to test for Voltage when the switch is:
ON (for 24v) as well as the OFF (for residual voltage)
OFF (for 24v) as well as the OFF (for residual voltage)