THIS WOULD BE A GREAT GIFT FOR YOUR FAVORITE TRANSFORMER BASED MODEL RAILROADER.
Using the speaker/circuit board from Gunrunnerjohn, I was able to mount them inside the Lionel GP7. Running on just a ZW and O-27 track, the diesel sounds mix in with the track noise and buzz from the E-unit but are plenty loud enough with the speaker at full volume.
Wiring is simple. It comes with a female connector for a two pin terminal or male plug. I didn't have one so I snipped it off and soldered it onto the same posts on the motor and E-unit that the lamp was soldered to. The polarity of this connection determines if the ZW whistle actuator is a horn or if it toggles the Bell On/Off. The sounds are realistic and rich. Nothing tinny or post war-ish sounding.
The speaker has a nice postage stamp sized flat area for mounting and comes with 2 sheet metal screws. The circuit board also has right angle mounting bracket that is tapped for a fine threaded screw. I had a #4 screw of unknown TPI that did the trick. So it's a total of 3 holes.
Positioning the speaker holes was tricky as the thickness makes a tight fit inside the GP-7 body. And there's a slight backward tilt. I biased my mounting position a millimeter and it fit nicely. I made a paper template the size of the speaker's mounting surface and using it made positioning precise.
Positioning the CB is simple but one must think in three dimensions as it has two capacitors that stick out at the top of the board. Also, the height of the board is about has high as you could get and still fit inside the body. It also needs to be centered width-wise. I was sloppy and missed the center by 3mm and that made for too tight a fit with the body.
The last detail to take into consideration is the locomotive plastic fuel tank. Accessing the chassis to install the screws from the bottom meant removing the tank. On my GP7 that's a one way operation as it breaks off the tiny bit of plastic holding it in place. I solved this by putting a dab of GOOP on the three tabs inside the body for a mechanical attachment. So far so good. YMMV.
Paper template for speaker mounting screw holes. Red wire post on motor is second connection point I used for CB.
Slight backward tilt of speaker. Post on E-unit with white wire is where lamp is connected and where I connected the CB
Birds eye view of components mounted on chassis. Black CB wire soldered to E-Unit. Red CB wire about to be soldered to post with red wire on motor. This polarity gives you the bell sound for a transformer whistle actuator. Reverse it for horn. Note capacitors overlap with motor swivel controls but are high enough to clear.
Close up of volume control. This layout kept access to the control. If your's doesn't my unit came with the volume set at maximum (full clockwise from this perspective)
Video of all three sounds.