525 Sc stock thunderbolt ign. Was running great all day stayed overnight at the bar. Woke up next morning and was running back to the ramp when it just crapped out and died. Replaced pickup in distributor still no spark . checked coil checked module. Anything I'm missing what's left to go bad?

TB IV ignition I assume???

Check the ground connections for the ignition advance module. Both the module case and ground wire need to be grounded or you'll get a no spark.

Did you run through the Merc flow chart for a no spark condition???

We have not where can I find that

Check the rev limiter behind the ignition module. Gave me 3 weeks of hassle

This may sound too simple, but it's bitten more than one of us. Check the Kill Switch.

Kill switch is first thing I checked

Yup^^^^^ kill switch, if everything else checks out!! Bit me one time too for about 3 hours one day on the lake!!

the 525 SC had three different ignition / electrical set ups. The first year or 2 did not use the OVERSPEED ASSEMBLY and the later year of the GEN VI did not either. All the years in between used the overspeed assembly.

That could be your problem if you have that app. I have seen that part eat some techs lunch. Also it is no longer available thru Mercruiser or any aftermarketers FYI to everyone. Engine serial # is important to show what set up you exactly have.

You mentioned that you changed the ignition sensor assembly under the rotor. These have 3 wires (ground wire black lead with big eyelet) on the newer versions Merc part # 87-892150Q02 is this what u installed. If so that ground wire needs to have a perfect clean un painted / no corrosion ground to attach to. Try jumper wiring it to the negative post of your battery and see if you have fire then just as a test and for a good solid ground source.

Do you have a MSD box?? go to https://www.msdignition.com/page.aspx?id=3206

He reports stock T-bolt ignition set up so I would think no MSD.