Compression? VRO still in service? Spark must be able to jump a minimum 3/8 open air gap with bright blue snap. If not DVA check stator output. These early small bore loopers are not the best idlers
See this quite a few times with DIY repairs. Damages repaired but problem not fixed. Like a ol Chevy, ya fix the rusted rocker panel but dont address the drain hole which caused it to rust
The question is ..does it have spark? If so go ahead and try to repair, if not it could already be bad and not worth the time to try and repair. The wire can be coated in liquid electric tape for testing if worried about shorts
Replace both of these...
https://bpi.ebasicpower.com/shop/mercruiser-sterndrives/trim-system-parts/power-trim-control-panels/cam-control-box-for-mercruiser-mercury-mariner-34682
https://us.amazon.com/CONTROL-BOX-GLM-Part-Number/dp/B004AQZ7YO
Way overthinking project, just build the 5.7's stock. All the extra work is not hardly going to be seen on that big of boat. Be different if it had a performance hull
Check all your grounds...those points should last at least 25 years if they havent been filed or papered. Only use 400 grit crocus cloth and alcohol to dress them.
ABYC 10.8.3
Battery cables and other conductors size 6 AWG (13.3 mm²) and larger shall not be connected to the battery with wing nuts. There is a TSB from OMC to replace all engine connectors with locking nut and discard wing nuts.
You dont need to do anything with VRO harness. Unplug the tan wire off pack tied into overheat sensor, and retest as thats what triggers SLOW. Check the t-stat/poppet assy. The VRO's never had a feature to trigger SLOW, just horns and lights
