I'm going to document my process of adding sound and video to a 1978 Stern Nugent pinball.
We picked the machine up at a reasonable price in semi-working condition. After a few harness, connector & board repairs all was working well. We tore it down to the playfield, polished it up and replaced the lighting with LED lighting. The flippers have been rebuilt and now it is time to retire the blips beeps and bonks of the early Stern sounds. Ideally the pop bumpers will be a shot gun sound. The lane roll overs are going to be voice or sound relevant to the lane. We jhave not picked out the actual sounds for all switches yet.
The goal is to add a sparknet mp3 trigger for callouts to the pop bumpers and lane switches. I'm going to do this by stacking the switches to trigger the sounds.
For the drop targets I want to add video with the corresponding song.
We will be adding this to the Cat Scratch Fever drop targets, Free For all drop targets and a Stranglehold bonus target.
The video trigger will use custom brackets and switches added to the drop targets. For the video playback I am adding a small 5" display to the apron rather than the back glass.

The picture here shows the custom bracket 3D printed added to the drop targets. It is a simple rollover switch that is actuated when the third target is dropped and the targets reset.

Why am I choosing the components?
Why an apron display over back glass display?
I had the Mp3 trigger and the video trigger left over from a past unrelated project. They were sitting on the shelf collecting dust.
As far as the display in the apron it was far easier to add a display to the left side of the apron than rework the back glass and the head box interior. Used aprons are cheap so if it doesn't work out it is an easy fix to return to the previous condition.

Thanks,
Dave

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We 3D printed isolator pads to insert in the reed switches. This way we can stack the switches and not worry about a voltage transfer. The mp3 trigger just needs a contact to close to trigger the sound.
Found out it is real easy to add isolator pucks to the insulation reed to whatever height I need.
The 3D modeling was done in TinkerCAD which is an amazingly simple free online software. 3D printing is done on a Prusa printer.

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Thank you Jeff, I will check it out. We should have two sounds going at once. The video trigger also has sound. I'm using a small mixer to run both the MP3 trigger and the video trigger sounds into the amp at the same time. The video will play the "Sound track" and the MP3 will do call outs and switch sounds.
If I ever do this again it would be cool to be able to play more than sound from a WAV trigger. I am debating on the speaker placement. The cabinet is decent so I did not want to cut holes in it unless it was a last resort. I may do a speaker topper or have a speaker box that can attach to the bottom and be removeable.

First tests on the video switches today. It went well.

Here is the video: