ThunderBolt IV HEI Ignition System
run from mid 80's thru mid 1990's
The thunderbolt IV ignition system designed by mercruiser is by
far one of the most dependable systems to ever be on the market. Durable and simple to
test it has stood the test of time with remarkable performance over the years.
Below is the test flow chart which requires only a volt meter.
All tests should be done with a "KNOWN" good battery and test for voltage drop
at the starter first, then the ignition coil, during cranking, before proceeding with
these steps. (See minimum voltage page in directory)