If you have a single coil ignition system with Bosch coil you can try the
following (you may need a multimeter):
- With all cables connected to the coil primary windings, turn on the ignition,
and check the voltage between the terminal "15" of the coil and ground (chassis).
With a normal condition battery you should measure above 12 Volts.
If the reading is less than 11.3 Volts on terminal "15" that can be caused by
two things: defective primary winding (short circuit), which is overloading the
supply wire, or defect in the supply line (or bad connection on terminal "15").
With ignition turned off you can measure the resistance of the primary winding
between the coil terminal "15" and "1". The value must be between 0.5 to 1.5 Ohms.
You can also check the secondary winding resistance wich is 6 to 12K Ohms.
If any of the resistances out of the tolerance the coil must be replaced else
it's a supply problem.
- If the voltage is normal on terminal "15" and the resistances are also OK, check the
functionality of the power module. Turn the crankshaft to TDC position.
With ignition turned on measure the voltage between coil terminal "1" and ground (chassis).
The voltage needs to be around 0,7 to 3 Volts. If not, try to rotate the crankshaft to
any direction from TDC while watching the voltage. If the voltage rises then drops while
turning the crankshaft the ignition primary side is OK.
I hope this helps.