This is a drop-in Rectify speaker system for current-run BLI SD40 locomotives - both with factory sound or the DCC-Ready Stealth version. The speaker snaps into place under the rear PCB above the drive-shaft where the stock speaker fits. No modifications are required to replace the stock speaker (or install this one into the Stealth). You can reuse the stock 2-pin wire-harness or purchase the Small 2-pin 1.0 harness I have available in the PARTS category.
 
Optionally, the top weight screwed to the chassis behind the cab can be removed and a UFIT-5940-RC1 speaker can be placed here (at least on the Stealth versions). Use one or the other or both speakers!
 
Dimensions are 9mmH x 18mmW x 25mm