Guys I would caution pulling off plug leads. This can generate a back EMF and damage the ignition system. The correct procedure to do a power balance (that’s what your describing) is to SHORT out the HT not open circuit it. You can do this by pulling the HT lead spark plug end boot or by using a steel extension piece to the spark plug terminal (can be made with a slotted tube of thin metal) and shorting it to the cylinder head with a large screwdriver.
Crypton and Sun cabinets came with a box of such adapters. Google Gunson 77074 Spark Plug Extension Leads With Spark Tester
BR
Colin
