I have an old All-Pro ignition scope that uses direct series connection between the ignition coil and distributor cap as well as between the #1 cylinder plug wire and sparkplug. Each of these connections feeds through a 15.4 M resistor to the inputs of the scope. The primary connection on the coil switched side feeds directly.

Would anyone hazard a guess as to how I would upgrade this thing to use a capacitive input to replace the coil interface and an inductive clamp to trigger input (#1 cyl). I think experimenting with different timing light or tach pickups would suffice for the #1 probe as it is just a sync probe. The secondary connection needs to be calibrated for voltage.

The maker Rite Autotronics in LA is long gone and schematics are non-existent.

 

This http://www.ebay.com/itm/Ignition-Pr...gh-Voltage-Capacitive-Clip-Auto-/152543719316 may be a place to start. Get the real specs, not the Chinglish one.