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Electrical Mystery!


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Ok so really weird thing happened the other day - Id been out fishing all morning, starting and stopping the engine regularly and running live bait pump, lights, sounder etc etc and had absolutely no problem. Then I headed back in to one of the harbour wrecks and anchored up along side another boat, when I started to swing around too close to him I started up and motored forward and cut the engine, 10 mins later I went to do the same thing and absolutely nothing happened when I turned the key!! Tried my electronics and they wouldnt work either. Weird because I had not been running any electronics since the last time I started so definately not drained (and it had only been 10 mins anyway). thankfully the other fisho was just about to leave so gave me a tow back into the ramp, thanks again if your reading this mate!

When I get home I turn the key again and the tacho slowly starts to light up. 'Oh good, it fixed itself!' I thought to myself but then when I fully turned the key as if to start the engine the tacho just went blank. Same thing happens every time. When I turn on the nav lights they light up but only very dimly, a fraction of what they usually do. The bilge's wont work and if i try turning them on when I have the key turned so the tacho lights up then the tacho drops out.

I have remved the battery and connected my car battery and the exact same thing happens so it is not the battery.

I had recently connected a battery isolator switch but I took that out of the equation with the new battery and still the same thing so I dont think that is it. The terminals all feel tight at the battery and the isolator so not that either.

What else should I be checking? Prefer to fix it myself if can rather than take it into the shop (Yes Huey will be my first point of call if I cant do it!)

Thanks for any help or tips fellas - have a good easter!

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Sounds like you have a high resistance joint somewhere ( it wont allow the full flow of power ). Check all connections to make sure they are clean.There is a small terminal/ post brush that you can buy from most auto parts stores. Clean the terminals and lead connections , and try to start the engine. If it is still doing the same thing you will need to look further. Are the fuses clean and tightly connected ? Also check the electrical connections at the starter motor while you are at it .


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Sounds like a bad connection.

Check ALL of the connections in your battery cables, make sure they are clean and tight:

1. Terminals,

2. Lugs, isolator lugs, starter solenoid connection as it is commonly used as a junction post.

3. Earth cable / lug on engine block.

4. Condition of your cable at all of these areas (does it have corrosion in the copper?)

5. Follow all battery cables and check no one has put a joiner in previously. (they tend to attract corrosion)

Remember to check any earth connections as well as they are as important as the positive cable.

You could also check to see if the cable or connections are getting hot when you attempt to start it. (would point to the fault).

Hope this helps. Good Luck.

Edited by aquaman
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Thanks guys will give all this a go when I get back from Easter get away. None of the cables are hot because nothing happens when I turn the key! Also, have bypassed the isolator already so will give the other things a try when I get back. Its just weird that it happened after working fine all morning...

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Good luck with it dicko,

I had a similar problem with my boat however it didnt effect the starting of the boat but none of my lights worked luckily it ended up being a rusty fuse the old glass type but yours sounds like one of the main power cables or even a earth wire just make sure you have a quiet place to work and go through the wiring from your battery and I hope that you find it sooner rather than later I know my problem is not the same as yours but use the same principals and you should come up good and the fact that you are losing power to everything hopefully means that the fault will be close to the battery where all the wires join together could even be as simple as the terminal's themself dont overlook anything..



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maybe when you moved and cut the motor it is still in gear,check prop is free spinning though highly unlikely but i have had gear cable snap and out on the water and it looked like it was in neautral but nothing would happen when you turn the key,though that dosent explain why your lights are dim,try just connecting single things to your battery with no engine cables going to your battery,like radio ,lights and see if they work individually ,they should till you find the culprit ,ie radio, bilge or the engine cables to narrow the prob down to the 1 area .but it sounds like a bad short somewhere ,could be your rectifer you can do a visual check and see if it has any heat marks or a slightly melted look.it is a process of elimination now please keep us posted to what you or huey find cheers dunc333

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Dicko's up and running again now. I met up with him yesterday and helped him get it sorted out.

In summary, most of the posts here were on the right track.

No problems with his new battery switch. The switch and cable size was fine to handle his 50hp motor. His sparky mate had soldered the cables for him, but it was hard to externally see how well the solder flowed. (seemed functional)

Under the hood, all the wiring was firm and in good order.

The previous owner had installed a home brew buss bar/distrubution box. The way it was done was electrically efficient, but I considered its design and placement a bit unusual :wacko: especially for a marine environment. We cleaned up some suspect joints, re crimped a few lugs, re-seated the main accessory fuse and pulled out a number of corroded terminals that were no longer used.

The currents flowing much better now. The starter is apparently cranking over without hesitation and much faster than before. His alterrnator seems to be working fine. Mid 13 volts and pumping nearly 5 amps into the battery around 3000 rpm. (didnt want to rev it too hard on muffs) Incidently if anyone is interested, accordng to a clamp meter the starter motor drew a stable 65-70 amps once actually cranking. The initial inrush current draw was an indicated 100'ish amps but im not sure how accurate this particular inrush measurement is due to the very short measurement period.

There is a good chance that we have solved the issue he posted previously with his sounder shutting off when cranking the motor.

Whilst there are a few odd wiring improvements I suggested he makes as time and finance allows, his electrics work and he is back on the water again. Apparently he has a plan to terrorise Jewfish ? :thumbup:



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Yes all fixed now, and I must say that when there is someone that knows what they are doing looking at it, it stops being classed as a mystery! Rod rocked up and found the problem within about 30 seconds! I have to say a massive thanks to Rod, came all the way from his house to mine to sort it out on the public holiday! What a top bloke! We had fished together a few times previously (last trip was the Hairtail social in 2007) and I even caught my first kingy on his boat way back then! I owe you a few beers I think Rod, and I look forward to our loosely planned trip out to the peak to chase some winter kings!

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