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Old 11-25-2021, 04:31 AM   #1
City: Pensacola
Vessel Model: 1979 Mainship Mark I
Join Date: Nov 2021
Posts: 1
Engine auto start

While checking on my 1979 34 ft. Mainship after getting home from out of town business I found my Main Engine Running. Yanmar 4LH-DTE. After investigating I found that the starter ingaged to start until all wires burned up. Little damage to flywheel but starter and wires are Tost. The cooling seawater piping passes within inches of the starter and I belive if it had been rubber instead of fiberglass it would have burned up and caused water to flood the boat.
Anybody have ideals on what could have caused this. All ignition switches are new. No wires touched before this happened.
Weird? ?
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Old 11-25-2021, 07:45 AM   #2
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Join Date: Jun 2008
Posts: 4,404
Once in the 70s I was in the factory where I worked and a backhoe that was there the day before digging a hole for a machine base started on it's own. I saw the headlights flash then it fired up. The starter relay shorted out.

Once in my driveway the 1970 Dodge Dart I had tried to start on it's own. It was backing up out of the driveway on the starter motor when I ran outside and pulled the battery cable. The starter relay which was mounted below the battery tray and corroded and shorted out.
Jay Leonard

New Port Richey,Fl
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Old 11-25-2021, 10:23 AM   #3
City: Tampa, FL
Join Date: Nov 2013
Posts: 626
Just to elaborate on jleonard's comments... Something, somewhere HAD to have short-circuited. Switch, wires, solenoid, something!

Good luck finding it!
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Old Yesterday, 08:12 AM   #4
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City: Between Oregon and Alaska
Vessel Name: Charlie Harper
Vessel Model: Wheeler Shipyard 83'
Join Date: Jun 2016
Posts: 2,531
The problem has to be in the circuit that activates the starter solenoid. Probably a relay. Relay will be on or near the engine.
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Old Yesterday, 12:19 PM   #5
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City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,188
Seen a few boats do this. Common cause was an ignition or start switch on a flybridge or uncovered console. Water works its way into the switch and corrodes the contacts. Eventually they bridge and energize starter.
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Old Yesterday, 02:08 PM   #6
Senior Member
City: Grand Rapids, MI
Vessel Name: Arcturus
Vessel Model: 1973 Concorde 41 DC
Join Date: Sep 2020
Posts: 224
Had a similar thing on an Olds Ciera. Going down the highway it made a loud grinding noise for about 30 seconds. As I was slowing to pull off the road the noise stopped so I kept going. When I got home I shut down and tried to restart, no click, no nothing. The starter had energized itself and it spun itself to death with the car going 70 at the time. Had the starter replaced and the shop could not explain how it happened. Said they'd never seen it before. No shorts or wiring problems found, it had to be internal to the starter solenoid. Drove that car for a couple more years and it didn't happen again.
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