Have a 85 Thunderbird Formula with twin 350's. Last weekend change Cap an Rotor. Noticed rust on sensor so lightly sanded clean. assembled. Did timing, good to go. The port cap was torqued to the max. This weekend ended up getting cap off, did the same as last weekend, assembled. Wont start. WTF . thought it would be a nice day on the water. Boat still in driveway. Took cap off, took sensor out, cleaned well. Pulled center wire off, check for spark. Nothing. Bought a new coil. Installed. Turned ignition key, checked voltage on positive side of coil, 12.4v. Pulled spark plug wire off, installed plug and turned motor over with plug near ground, no spark. Anybody no what I did wrong to ruin my nice weekend? Boat ran fine Tuesday and Thurday. Any advise Please

What you did wrong is clean the sensor, the rust means nothing they're magnetic pickup and read through rust. They sound like the old style and once you disturb them they seem to stop working. New sensor and it should start right up. I would replace them in both engines.

i trouble shot my 350 mags until i thought my head would explode...things worked, things didn't.....it, ultimately was an ignition module...no problems since....

i tested it by swaping the mods...yep, that did it!..
c

troubleshooting guide.
http://www.marinemechanic.com/site/page251.html

Figured it out sunday, the steel square in the sensor was fliipped 180 from sanding. started right up. BUT, after setting timing in driving and launching boat. Motor had no power when hit throttle, just bogged down. So drove to shallows on 1 motor, anchored and checked timing. got it set at 8 degrees BTC, starts and idles, sounds like its missing. Hand feels like major arthiritis from getting shocked thru distributor while setting timing. New wires on the way. Ill change plugs and wires thursday and see what happens.