Whelen Deck-Master Strobe Project, Synchronizing in strobes 1987

Update video: https://youtu.be/rHmTRCf8zvE When Whelen Engineering released the strobe Dash-Master in 1987 the literature stated that two units could be tied together to make a "Deck-Master" which essentially synchronized the two units. Any two units could supposedly achieve this with the right cable. That either didn't materialize or was quickly discontinued because units released very early on and until the product was discontinued rarely had this feature. In fact it was rare enough that it is possible that only units purchased as a pair for this specific purpose were properly equipped. Regardless of the purchasing options the synchronization feature was discontinued several years later. The product remained available from Whelen as individual units until approx. 1996 when it was handed off to Galls Inc. and sold as part of the "Street Lightning" brand until around 2000. This video first walks through the background info on the system before documenting an attempt to make a Deck-Master system from two early units, one with the necessary circuitry and one without. This required reverse engineering the synchronization system and adding the missing components. This method of synchronizing two self-contained units was not used again by Whelen and there is little documentation remaining surrounding it. The way the first generation of Deck-Masters were constructed (with 555 timing chips) apparently necessitated a four wire system. Earlier and later synchronized deck and dash strobes simply used external power supplies. In 1998 Whelen did offer self-contained S360 beacons that could be synchronized, but with a different method of tying them together. I have a video showing an example https://www.youtube.com/watch?v=uNeYb6n_SuE There are a few electronics terms and concepts that I am a little "loose" with for the sake of having a video of a reasonable length and due to my lack of expertise, so please pardon any incorrect (but ballpark) terminology. The goal is to explain the system, not give a class in electrical engineering (check @ElectroBOOM for that). Special thanks to @drfrankenstrobe4055 (eLightbars.org member RS485) for handling a large portion of the electronics side of the project.