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2001 Shadow 600
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Discussion Starter #1
Please see image. I have my plugs coming in front the top, and I’ll connect the wires in from the bottom. Will this coil function free floating? Or do those bolt holes not only act as my securing point but also a ground to the frame?

In the middle of bobber build, looking to relocated rear coil and might just zip tie it down to my chosen frame position if possible so I don’t have to drill new holes. Thoughts?

thank you!
290771
 

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1983 Honda vt750 Shadow
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14,703 Posts
I don't think the coil windings need a ground- it is like a transformer, but if in doubt, wrap a piece of wire to the bolt hole and down to the frame in case there is no spark at least temporarily as a test.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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I see the eyelet loop to the core at the bottom of the coil picture.
If it didn't have to be grounded why would that be there?
 

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2003 VT1100C Spirit
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139 Posts
Isn't the ignition coil grounded through the spark plug? That's what makes the spark, right?

The wiring diagram in a Honda Shop Manual will tell you how the rectifier is grounded.

So...it sounds like you're customizing your bike...pictures will be expected!

🔧 📷
 

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1999 Shadow 750 ACE VT750CD3 Modified
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3,039 Posts
Isn't the ignition coil grounded through the spark plug? That's what makes the spark, right?

The wiring diagram in a Honda Shop Manual will tell you how the rectifier is grounded.

So...it sounds like you're customizing your bike...pictures will be expected!

🔧 📷
Despite how strange the twin plug and shared coil is, there is only one wire from the high tension side of the coil from each spark plug to the center electrode.
The ground maybe also required to kill EM emissions or noise, since electronics including the ICM don't like that stuff.

The regulator/rectifier definitely needs a physical ground and the some of the stock Honda ones actually dump heat using the the frame as a heat sink.
 

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The rectifier needs a physical ground? (though I do think it's a good idea) I do not see that on the schematic other than the Green wire(s) go directly to frame ground.
 

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1999 Shadow 750 ACE VT750CD3 Modified
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My memory may be playing tricks on me, but the one from my 750 ACE, (without fins) that I pried apart appeared to use the back plate as a ground internally it may have just been used simply as a common (-ve) of course. It then sandwiched an aluminum plate to the steel battery box to dissipate heat.
The ElectroSport one I now use as its replacement specifically doesn't care and also only relies on just the front fins for cooling so it could go anywhere as long as it had air flow.
 

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2001 Shadow 600
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Discussion Starter #9
Yes, with the coil I assume the ground is achieved through the wires and not through the mounting holes. We’ll see though! I’ll let you know if it starts.
Thanks guys
 

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1983 Honda vt750 Shadow
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One important function of bolting to a bracket or frame would be to act as a heat sink for the iron core and coil assembly.
 

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I am not seeing how the ignition coil can work without being grounded.
290793

Aren't we talking about two circuits ( for two plugs) being served by two two high tension wires and two primary connections like in the above picture? Both primary and secondary need to be grounded, no?
 

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2001 Shadow 600
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Discussion Starter #12 (Edited)
Again, I think the confusion is coming from specifying the method of grounding the coil. Of course the coil does need a ground, but my theory is the ground is achieved through the wire and not necessarily the securing bolts.

And like swiftly said, the securing function might also serve an additional purpose of heat displacement which may very well be the case and I’ll take that into consideration for my final placement decision. The question is moreso; will this coil function without being secured through those securing points/eyelets/holes (whatever you want to call them). And so far I’m not seeing any evidence that it will not function properly.

Anyone see something I may be missing? Thank you
 

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2000 Honda Shadow Spirit VT1100C
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3,359 Posts
Again, I think the confusion is coming from specifying the method of grounding the coil. Of course the coil does need a ground, but my theory is the ground is achieved through the wire and not necessarily the securing bolts.

And like swiftly said, the securing function might also serve an additional purpose of heat displacement which may very well be the case and I’ll take that into consideration for my final placement decision. The question is moreso; will this coil function without being secured through those securing points/eyelets/holes (whatever you want to call them). And so far I’m not seeing any evidence that it will not function properly.

Anyone see something I may be missing? Thank you
Coil body does not need to be grounded. Back in the old days, a car's coil was attached to the firewall of the car with a strap that secured the Bakelite coil body with two screws.
 

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Coil body does not need to be grounded. Back in the old days, a car's coil was attached to the firewall of the car with a strap that secured the Bakelite coil body with two screws.
It's true, but those old style coils had three terminals, and the positive side of the primary was the trigger.
290798

The style used on the Honda places the trigger on the ground side of the primary. My understanding is that one coil terminal is B+ and one goes to the ignition control device, where interrupting the ground will produce the spark. If this is the only ground and it's interrupted for the spark event, I'm having trouble seeing how the secondary voltage can be generated.

I'm probably just not understanding the system. You will try it and let us know?
 

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2001 Shadow 600
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Discussion Starter #16
Yes, I will try and let everyone know if I get shocked or not. I do have a trip coming up near the end of the week, if I cant get to it this week ill report back early November with results

Thank you!
 

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I think this diagram is very close to Honda's setup. Called a "dual spark"
290799

This apparently shows the only grounding of the secondary as being at the engine head (spark plug bodies), so I guess it should work? What do the diodes do? I assume those are built into the coil assys?
 

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1983 Honda vt750 Shadow
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Here is the coil Honda is using that is just the same as a transformer. Nothing needs to be grounded for the windings, but the plugs are in series and the head is the ground path for both. One plug fires in reverse.

A lot of cars use this system called a wasted spark because it fires on 2 different cylinders and the one cylinder is on the exhaust stroke so it is wasted spark. An idea to help lessen emissions. Honda fires 2 plugs in the same cylinder.
I don't know why a diode would be used, maybe to control cross feed in the one coil setup , none of the Honda bike manuals show that. with 2 separate coils.
 

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I don't know why a diode would be used, maybe to control cross feed in the one coil setup , none of the Honda bike manuals show that. with 2 separate coils.
Thanks for the diagram!

I was thinking perhaps the diodes are to prevent the possibility of generating a spark when the ground is restored to the primary after the spark event? Seems like the magnetic flux and hence the electrostatic polarity would be reversed from spark generation?

Another question I have: I noticed on the schematic, that the trigger wire from the ignition controller to one of the coils for my '96 Shadow 1100 is routed to the fuel pump relay. What does that do? Pulse the fuel pump as a crude form of duty cycle control?
 

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1983 Honda vt750 Shadow
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The relay is a safety shut off. When the engine runs the relay gets that coil signal.
If the bike would fall and the key is still on, and the engine stops, it shuts off the pump .
 
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