Topic: Use frame as ground?

[smccloud]

Does anyone know if it will cause a major issue on my '72 CB750K if I use the frame as the ground instead of running a seperate ground wire?  I mean, the ground terminal on the battery connects directly to the frame and no where else so the ground wire(s) have to connect to the frame somewhere too right?  I have to re-wire my bike as it is so I'd like to do something to make it look a little neater (at least in my opinion) plus I want to use the smallest weatherpack connectors I can (yes, I'm going overkill on most of the wiring).

[cobra2411]

Don't see why not as long as you have the factory battery ground on the one engine mount/frame point.

Oh, I have weatherpacks on my bike so you won't be the first... 

[smccloud]

Don't see why not as long as you have the factory battery ground on the one engine mount/frame point.

Oh, I have weatherpacks on my bike so you won't be the first... 

I'm just glad I don't have to buy a weatherpack crimper. Just wire & ends. Should be "fun" to build a wire harness from scratch though. Also glad I can "con" my dad into welding the nuts on for me, I can't weld worth a damn unless someone else sets upbthe welder.

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[HondaMan]

Keep this in mind when using the frame as ground: the welds at the frame junctions were not intended to carry currents. The steel used in these frames was not coated on the insides, so electrolysis is a factor in the life of the frame. This is why Honda went to the trouble of making a separate Green Ground circuit for all the lights, and a separate heavy ground directly to the engine for starting (all Japanese car manufacturers do this, also, and Ford started doing it in te late 1980s). Those engineers hated to spend a single cent on anything they didn't need to, so just the fact that the copper was used in the harness indicates clearly that they thought the frame was suspect for grounding use. 

[crazypj]

HondaMan brings up a good point.
 Using negative ground will cause electrolysis
 I had heard it (and not Lucas being contrary) was the reason British bikes used positive ground?

[paulages]

Electrons prefer to travel - to +, but re-wiring an SOHC to positive ground seems a but silly. I always thought the Brits used positive ground because no one really understood electricity back when the 6V and eventually 12V systems were designed, and there was simply no standard. In any case, it does seem that the British had it right in that regard.

Regarding the OP's original question: Back when electricity was not so well understood, the frame was relied on as a return path to "ground." There's a reason harnesses eventually included a "ground" wire, like Honda's green wire as Hondaman mentioned. Electricity simply wants to get from point A (+ side of the battery on our bikes) to point B (- side), and we're asking it to do a little work along the way. This is why it's called a "circuit." It's a loop or it doesn't work. When you ask the electrons to pass through rusty, painted, powdercoated, or poorly connected metal, you're going to see resistance and therefore a drop in voltage. If you want your electrical system to work as well as possible, give those guys the super-highway Honda gave them, which is the green wire circuit.

The big wire that goes from the - side of the battery to the frame is not just for the high current of the starter to return through... you need a nice clear path for the ignition as well, or you won't get spark. Try rubber mounting your entire engine and see what happens. You need the electricity arcing the spark plug electrode to make it back to the battery as well! I like to run a wire from the top of the engine into a loose green connector beneath the tank just to be sure.

Don't go back to the '30's in an attempt to "simplify" things!

[gane]

SMCLOUD, Double check your' FSM. To the best of my rec. ALL Honda's  with electric starters run the neg, battery cable to cases., then from wiring harness a few smaller guage wires to chassis. & in some cases none at all, counting on frame to engine to suffice. The heavy guage wires from battery to ground, & on the otherside, to starter sol. & starter motor  are "stout" because the starter draws "big AMPS'" compared to the rest of system. The Japanese in their wisdom decided the Green should be "ground" or "earth", don't be shy, Just because the wiring diagram doesn't show it, tagging a Green wire at tailight , coil area, inside h/l bucket does no harm.  I've spent hours trying to figure out just exactly why certain circuits are as they are, & my best guess is that it was the cheepest to manufacure. Still. inspite of their umbiquity, It's easier to trouble shoot a stock wiring harness than a  PO's buchery. luck G

[smccloud]

SMCLOUD, Double check your' FSM. To the best of my rec. ALL Honda's  with electric starters run the neg, battery cable to cases., then from wiring harness a few smaller guage wires to chassis. & in some cases none at all, counting on frame to engine to suffice. The heavy guage wires from battery to ground, & on the otherside, to starter sol. & starter motor  are "stout" because the starter draws "big AMPS'" compared to the rest of system. The Japanese in their wisdom decided the Green should be "ground" or "earth", don't be shy, Just because the wiring diagram doesn't show it, tagging a Green wire at tailight , coil area, inside h/l bucket does no harm.  I've spent hours trying to figure out just exactly why certain circuits are as they are, & my best guess is that it was the cheepest to manufacure. Still. inspite of their umbiquity, It's easier to trouble shoot a stock wiring harness than a  PO's buchery. luck G

No matter what, I need to build a new harness.  I'm the one that's done most of the harness butchery

I can find '69 - '71 and '75 on harnesses, but none for a '72

Beeped from my Droid R2D2

[CBDee]

I guess I don't understand whats being discussed here, bit ive allways been told I must scrape paint to get a good ground, especially where the green wire attaches and Honda scrape's the paint at the coil mount and other places. If the frame isnt being used as a ground, why is this necessary? Wher does that big green wire attach? I 'm confused. 

[paulages]

I guess I don't understand whats being discussed here, bit ive allways been told I must scrape paint to get a good ground, especially where the green wire attaches and Honda scrape's the paint at the coil mount and other places. If the frame isnt being used as a ground, why is this necessary? Wher does that big green wire attach? I 'm confused. 

As already mentioned above, the current to the starter and to the spark plugs both rely on the frame to return to the battery. The coils themselves don't "ground" to the frame at all, but there is a big green loop there on some models that ties the green wires in with the frame.

Think of it this way: A simple electrical circuit is like a racetrack. Current begins at the start line (we'll call the start line + and the finish line -), flows in one direction, and returns to the finish line. Somewhere in there it does some work... turns a light bulb on or whatever. For the sake of this analogy, pretend that the track is painted black for the first half and green for the second half.

Now imagine that there are side roads along the way that are all one-way and end up meeting back on the track at some point.... (pits maybe?). The starter is a big fat monster truck and needs a really wide side track. However the path gets from start to finish doesn't matter, but you can see that the main track- the shortest route from start to finish-  is the easiest route. If we ask the rider (current) to go down a muddy, bumpy road you can see that it will be harder to return. This is what a rusty, painted, etc frame can act like if we are asking it to be a return path ("ground") to the battery.

Anyway, I'm no electrical guru, but that's how I understand electrical circuits on our machines. Cleanest, quickest route from + to - is best.