Uncommon Grounds

[posplayr]

What do the "77777" labels mean in that diagram?

I kept looking and could not figure out what you were talking about............


Then it dawned on me; that is the "pitch fork" symbol for a "frame ground"

[MisterCinders]

I kept looking and could not figure out what you were talking about............


Then it dawned on me; that is the "pitch fork" symbol for a "frame ground"

Why does the frame have one then? Or is that to indicate where the other pitchforks link to it?

IOW, the battery has a fork because it's connected to the frame. The load has a fork because it is connected to the frame. The frame has a fork as well, to show where paths that end in the other two forks pick back up.

[posplayr]

Why does the frame have one then? Or is that to indicate where the other pitchforks link to it?

IOW, the battery has a fork because it's connected to the frame. The load has a fork because it is connected to the frame. The frame has a fork as well, to show where paths that end in the other two forks pick back up.

The way you interpret it is that anything with a pitch fork is connected together via the common "frame ground".

So normally the frame pitch fork would be understood(not shown), I just wanted to be able to explicity create the current path for all return currents. Because it is normally not shown, this maybe where a lot of people get the idea that the current is absorbed into the frame. Reality is that it has to get back to the source.

[Normk]

Motorcycle manufacturers switched to a common harness ground about 3 decades ago mainly because it made for quicker assembly. Automobiles continue to use multiple frame grounds because of the longer runs required. The easy answer to your grounding question is that, generally, motorcycles tend to have excessive voltage drops in the common ground circuit due to the headlight load.

A quick voltage drop check between the headlight bulb ground terminal (left side of the bulb's three terminals) to battery negative with engine running and headlight on high will indicate the loss in the ground circuit. If showing more than 0.2 volts, I usually install an additional ground between the headlight ground terminal in the headlight plug and a frame bolt near the front.

The additional ground serves several purposes since it removes the headlight load almost completely from the common ground circuit, other loads which remain dependent on the common ground are at a higher voltage. In addition, the ground path is shorter for many components which ground "forward" through the additional frame ground rather than to the original common ground point.

It can be quite illuminating to monitor the direction and degree of current flow in the ground circuits of some bikes before and after adding additional ground(s).

A separate but similar subject is that of voltage drop in the insulated/positive side of the harness. Some machines exhibit quite high voltage drops in this area also but the way to reveal is to do a series of voltage drop tests in order to measure the degree and to locate the drops.

One of the most ignored means of reducing voltage drops/losses is to reduce circuit loads by use of LED or HID.

Use your voltmeter to detect and locate voltage drops in areas such as connectors before attempting to correct imagined issues through blind cleaning. Once you have a reference and location for a poor connection, revealled by a high voltage drop, the correction can be verified by rechecking voltage drop in order to determine whether the issue has been resolved.

[daturat100r]

The term ground prob came into use in days before motorcycles existed.Always wondered as a kid why they only had one wire going to the old milking shed before it burnt down.With reference to the bikes electrical system the frame is ground and any resistances is not good so using an extra earth harness along with change to negative earth greatly helped reliability.Positive earth systems actually promote corrosion of steels with the current flow in same direction as the oxidation reaction whereas negative earth inhibits further corrosion even though steel to copper connections are common.
Electrolytic corrosion protection is commonly used with steel in boats, structures pipelines etc