I'm trying this too!
Ed,I started having some starter solenoid trouble on my '76 Hunter 30 last year. After a few weeks of "maybe" starts, the power contacts of the solenoid gave up altogether, meaning I could hear the plunger in the coil move but the starter motor never turned.After pricing the new solenoid or starter package, I decided to try and cheap out. I got a bulkhead mount solenoid from a local auto parts store for 10 bucks. I first wired it kind of like you describe I think: with the ignition key switch energizing it and some heavy cable in place that basically paralleled it's closed contacts with the ones that were bad on the original starter mounted solenoid.( Mines a Yanmar YSE12)I figured I still needed to leave the original solenoid in place and wired up since it's core/plunger is mechanically linked to the starter shaft that has to engage with the flywheel on start-up.Well I tested this arrangement with no diesel (throttle closed), the engine turned over but when I released the key and the start switch opened, the starter motor kept turning, some kind of feed back through my wiring/ground I guess that kept the new solenoid energized with the start switch open.I didn't think it would work, but I tried starting the motor with the wire from the start switch completely pulled off of old solenoid, (meaning the starter switch only energizes the bulkhead solenoid)and the engine turned right over, and correctly stopped when I released the key. When I opened the throttle and started, everything worked just fine.Although I was a bit uneasy about having just a bulkhead solenoid, when there was that obvious mechanical linkage that had to be there for some reason on the original solenoid. I ignored it for the rest of last season because it started everytime.Of course these things always catch up to you. This year, and getting more frequently all the time, when I go to start the engine, the starter motor is energized (I can here it spinning and there's the corresponding voltage drop) but the starter spindle/shaft doesn't always engage with the engine flywheel.Usually after a number of rapid fire twists of the key switch, the starter spindle for some reason decides to cozy up to the flywheel and she takes off, but I'm now looking to make it work everytime reliably.Even if I do spring for rebuilding my starter/solenoid or a new one, your experience (and mine as well) has always been that under certain voltage/ contact condition / wiring-terminal arrangements, I'll still get the occassional "no start" happening.For that reason I'd like to keep the bulkhead solenoid in the circuit after I get the starter mounted solenoid functioning.Did you ever encounter the problem I described with the bulkhead solenoid staying pulled in even after you released the start switch?Is your original solenoid completely out of the circuit now? I hate to make you explain it again but could you give me the spoon feed again on exactly where you made your wiring terminations? You can leave out the sizes/colors I'm just trying to figure out how my arrangement has a kind of "holding" circuit for my bulkehead solenoid and yours does not.