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grounding mags

jpatter123

jpatter123

Well-known member
well I am wiring everything up and was curious on where to ground the mags. All my negatives on the boat run to a bus bar (just the way I prefer to wire). A buddy came by tonight and said run your mags right to the bus bar and at first I was confused because I thought I needed an earth ground to ground out the mags. But after further thought the bus bar runs to the negative terminal on the battery which goes right to the motor block so its a combination earth/negative ground , correct? If this is right then it should work or am I going about this wrong? I orignally was going to ground right to a stringer on the hull figuering this would be the best earth ground but its not a great 12 volt negative ground. its an all aluminum boat.
Also what size should the ground wires be? It looks like 8 AWG coming out of the mag and 14 going to my switch. But the ground side the guy had it with what looks like 16 or 18. I was going to replace this with 10 AWG. Is this unnecssasary? Thanks.
 
I will let some one else answer your other questions but as far as grounding a boat does not have a earth ground and even know it is done and will function you should NEVER ground anything to the hull it should always be grounds by wire back to the battery or in your case to the fuse panel at the Neg witch is ground wired back to the battery.
if you where to ground to the hull or stringers you are asking for electrolysis
 
I like to use a separate ground wire running from each mag to the switch, usually mounted to the plug wire block. This is the best way to me as you are not relying on the mag mounting bolts for a ground, as the rubber impulse mag couplers and gasket insulate the mag from the engine. I know it is more wires but I like the security of a solid connection.

Larry
 
The mag is completely independent of your 12 V electrical system.
and theoretically should be grounded to it's self.
the electrical impulse from the magneto will go either through
the points, and coil, and then on to the sparkplug, or take the
path of least resistance back to its self.
 
goldhunter_2":30zgx7ty said:
I will let some one else answer your other questions but as far as grounding a boat does not have a earth ground
Click to expand...

an aluminum boat sitting in water isn't considered an earth ground? I wasn't even thinking about sitting on the trailer.
I guess I'll just ground it like it was on my other boat to my metalwork.
 
just run one heavy ground wire form the battery and tie in all you grounds to that wire.

by grounding to the hull or the cage (it will function) what happens is that that power is looking to travel to the lowest point of least resistant to get to the ground for example; say you ground you spot light to the top of the cage that ground runs through the cage into the hull where it goes form the bottom of the hull into the water then to the ground when the ground is leaving the hull into the water it makes a reaction that eats away the metal
 
JP I would ground your mag separate to the engine case away from any other grounds on your rig . If you were to tie them all together and lets say you go to start your boat and the best contacting ground is your mag well you just fried it then because you just tried to start it through your mag ground.
 
Your mag is grounded out to the engine case. The battery is grounded to the engine case. Just do them separately. Don't hook your mag to the battery ground. Use a separate ground.

There is no earth ground in the boat because there is no earth to ground to unless you're running dry.
 
I got it figured out today. Talked shop with a few guys. Thanks gold for that info I honestly never considered electrolysis you definetly saved me there.
I think you'd have to see how my boat is wired to understand the grounds. The negative from the battery goes directly to the block. My bus bar is only for my lights and eletronics. But it ties right into the main negative cable. Its one of the cables that comes with the 2 guage negative cable but it also has a 10 AWG cable. The bus bar ties into the 10 AWG. The 2 guage to the block. What I was getting at is when I go to shut off the boat and need to ground out the mags I wasn't sure if I should have isolated it completely from the 12 volt ground.I understand how it works now so I am good to go.
I honestly think its been the 8 hour days at work and 7 hour nights of busting my tail to get the boat done for the wet weather has had me over complicating things. Good news is tommorrow should be my final wrenching day :headbang: Just have fuel lines, install two longer engine mount bolts and put the prop on life is sweet!
 
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