Have an old project that needs a new ignition switch but the mounting hole has a broken alignment tab (interlocks with stem to prevent rotation)?
I designed this for just such a problem on my golf cart. Simply insert the ignition switch into the bracket then into the rear of the vehicle's ignition switch opening. Place the faceplate onto it. Use the ignition switch stem's retaining nut to align the faceplate by simply screwing it on. Once fitment is verified, mark and drill your mounting holes, bolt the mounting bracket to the faceplate, sandwiching the vehicle's ignition hole in between, then install the ignition switch!
This bracket works specifically with the "87-17009A5 Boat Motor Ignition Key Switch For Mercury Outboard Motors 3 Pos S7R1" I found on Ebay. This switch DOES have the magneto kill connection (not important if you aren't running a magneto-type ignition system). Despite the pictures in the posting, this ignition switch I received has a square body. To be completely honest, I think they sent me the wrong switch. It better resembles one for a Yamaha outboard.
This only works with square bodied, short stem ignition switches. It may also work with long stem but I don't have one to confirm dimensions.
Mounting bracket dimensions: Sleeve inside is 35mm square. Outside is 41.36 square. Overall: Due to the area available for mounting, dimensions are 78.51mm square X 48.35 deep with ignition switch hole off-center. The mount's ignition hole is 21.36mm dia X 3.17 mm deep. Mounting holes are sized for 1/4-20 carriage bolts. Faceplate: 78.51 square X 4mm deep and letters raised 2mm from surface, totalling 6mm deep overall. The faceplate's ignition hole is 33mm, to allow switch's retaining nut to fit inside it.
Since my engine doesn't have electric choke, I'm using the "push to choke" feature as an accessories power button, triggering a latching relay (eBay description: "12V 1 Channel Latching Relay Module,") to activate/reset the circuit with the key inserted and turned off. Power will also be supplied by the ignition "on" connection (using a diode to prevent power from backfeeding to other circuits sharing that connection. eBay description: "12SQ045 12A 45V 12AMP Schottky Rectifiers Diode" or similar).
While I'm not going to bother, for easier reading of the labeling, you can pause your print once the top layer is finished and change filament colors. I used the ironing feature for the faceplate but it messed up the lettering so I'm re-printing it but the picture is included for representation.
I added a round faceplate, in case you prefer it over square.