It's decades since I've worked on a/c, but electrical/electronics doesn't change that much. A question
1) Is the exciter box electronic, or electro-mechanical ?
Ignition system are high voltage and require decent insulation. Heat and liquid or vapour are not good. As mentioned chaffing is also a problem.
Disconnecting the plugs (or pulling the cable off the plug) to check for spark can cause breakdowns as the generated spark voltage can be higher than it would be under designed operating conditions - This will send high voltage spikes back into the ignition system, causing damage.
Under these conditions, your best piece of test equipment .. is your nose.
High voltage/current carbon burns stink... sniff each ignition cable - the whole length of it (insulation breakdowns happen at a specific point) and sniff away at the ignition/exciter box... you'll smell burnt carbon/silicon here too.
Carry on sniffing the whole ignition path.. plugs included.
Edt: Silly me, I forgot to mention the most important aspect - Safety (which you'll probably know anyway) = make sure the whole system is switched off or battery disconnected before you sniff away, otherwise you might have your brains 'carbonated'.