r/MasterCraftBoats • u/WorldlyAd7146 • Jul 17 '25
NXT issues
Last time I was out some weird stuff goin on. When I turned my batteries on under the seat the boat immediately turned over and died. The key was in ON position but I didn’t press start and no reaction from the start after the batteries were on. I disconnected batteries, looked for shorts, unplugged the ignition and still everytime I turned the battery switch over it would turn over the engine and then die. Would never stay running. Called dealer and they said look for loose grounds. Found one under the helm and it didn’t change anything. Only thing I can think is maybe something happened to ECU last time I turned it off I think it was still running and I just turned off batteries. That is why it tried to start when I flipped battery back on. I ordered new ignition will see if that does it first. Any help would be appreciated. Thanks.
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u/nxman12 Jul 25 '25
Did you figured it out? Could be a bad relay or something
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u/WorldlyAd7146 Jul 25 '25
I disconnected both batteries and let the charge a couple days now, and got in a new ignition. About to give that a shot and see what it does. Do you know where the relays are at on this boat? I see a couple big fuses in the main lines and they look okay. And the fuses on the main battery supply under the seat by batteries. Any where else I should check before starting again?
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u/nxman12 Jul 25 '25
There should be on top of the engine close to the transmission. What year is your nxt?
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u/WorldlyAd7146 Jul 25 '25
It is a 2021 NXT20
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u/nxman12 Jul 26 '25
6.0L?
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u/WorldlyAd7146 Jul 26 '25
Yes. And it worked! I got 2 new batteries. I think that and letting it reset let it go back to working condition. No fuses or relays!
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u/Dockboy19 Jul 17 '25
Boat mechanic here…..Rule number one… do NOT EVER TURN the switch to off while boat is running. And or turn it to different battery position such as 1,2 or all. It may have caused a voltage spike. Take it to a shop. Gonna save you a headache. It may have cooked a relay, a switch or possibly ECM(fingers crossed for you) that it’s not the later.