The often quoted mystery box mentioned in the workshop manual.
Often worth hundreds of dollars.
Here is a simple diagram of one that works for those that can read a circuit diagram.
Would recommend a higher voltage capacitor but I was only proving signal from the trigger in flywheel so only a few volts.
Input on left and meter plugs in on right.
I used alligator clips to go on bike and separate banana plugs for my digital volt meter to measure the resultant DC voltage.
Don't be cheap and buy the 4 diodes and make a full wave model.
The push button is there to discharge the circuit so you won't get back EMF when you move the leads.
Can hurt or sit you on your a$$ when testing the coil input.
Hope this helps someone fault finding