Mercruiser thunderbolt iv ignition timing procedure. The advance is probably not full in at 2500. The Ignition Amplifier controls ignition coil primary current without the need of a resistor wire. Apr 14, 2002 · Find the ignition module, it will have an identification stamp on like 24R or 20R. As far as seeing timing marks, you just have to do what's needed to see them. Thank you. According to the mercruiser manual at 2000 rpm it should be around 12 deg advance. Connect power supply leads on light to 12 volt battery. Jun 20, 2018 · The Thunderbolt IV does not have a base timing mode. The document discusses several ignition systems used in Mercury marine engines: 1. 4 liter engine equipped with a Thunderbolt IV ignition. nuh 9d7d qeui db5ktqxv zl 28r8 glnca ckgpe yzwiy ye7w