Re: 67 thunderbolt 500 (help!!)no spark
The 4 cy merc 500 has a belt driven distributor. the wires going under the flywheel is for the charging system. Those wouldn't kill the spark, just the rectifier, and therefore the charging system. Most of them had magneto ignition with points. If you feed battery voltage into the single wire terminal on the side of the mag, you kill the points. That terminal is grounded to kill the engine. The spark plug wires screw into the cap, don't pull them out! There is also commonly a mercury switch to kill spark if the engine tilts up to high. It looks like a small brown cylinder with 2 leads, one is grounded to the single screw that mounts it the other goes to the mag. Disconect it to see if it is killing your spark. The points could be just corroded or insufficient gap. However the gap is supposed to be small, like .006 or .010 I don't remember without grabbing a manual. Some have the specs stamped into the housing.
If you have the rare (for that age) electronic ignition then I believe it has an external module on the front cowl in front of the carbs and an external coil. You could do some expensive damage to those components. Stuff you may have difficulty finding. You can install a standard Mag in its place.
Hope this helps, Dave
