Engine wiring question....what is this?

[four winds]

Some near simultaneous posting going on. All good.

Nothing on my Yanmar harness matches the standard. No solid yellow at all, anywhere. Other standard colors mentioned not the same either.

The shielded wire is curious, but likely chosen for the color (Out of the scrap wire box). The shield isn't grounded.

Not connected "between" to wires. Merely tapped off a convenient switched 12v wire.

Which contact on the alt does the wire go to? Charge lamp? Field?

The only wire on the contact?

[rwidman]

Originally Posted by four winds

Some near simultaneous posting going on. All good.

Nothing on my Yanmar harness matches the standard. No solid yellow at all, anywhere. Other standard colors mentioned not the same either.

The shielded wire is curious, but likely chosen for the color (Out of the scrap wire box). The shield isn't grounded.

Not connected "between" to wires. Merely tapped off a convenient switched 12v wire.

Which contact on the alt does the wire go to? Charge lamp? Field?

The shield might be connected at the other end.

There is no possible way to figure this out over the Internet. Someone who knows what he is doing has to be there and trace the wires and then try to imagine what someone was thinking when they concocted this "circuit".

In the meantime, it's a fire hazard.

[cptcptcpt]

if you can put a meter on them with power off and then again with power on it may give a few clues

[four winds]

Maybe I can't figure it out over the internet.

But we haven't even gotten to twenty questions yet. And we almost have enough info to draw the circuit diagram.

I'd bet a dollar someone here will know exactly what it does then.

I'm not a lobbyist for pro techs or a safety nanny. I just like puzzles. Pretty sure I'd wrap some tape on that jewel in the mean time, though.

[Seawindii]

Could be a home grown noise filter if the larger component is a capacitor. A cap will block A/C type noise on a DC circuit so will filter out hum/buzz on a stereo, for example.

[mrybas]

It's a cat, so there's two engines and they're both wired the same way.

I put some heat shrink tubing over it for now.

[four winds]

Seawindii's stereo "whine" filter sounds like a possible candidate.

It is a capacitor. And a diode. And connected to the alternator.

[Cheechako]

Likely a diode which dis allows current to feed one direction. Usually for an alternator. I forget what the function is...

[rwidman]

Originally Posted by four winds

Seawindii's stereo "whine" filter sounds like a possible candidate.

It is a capacitor. And a diode. And connected to the alternator.

Well if it's a capacitor, it's not going to pass any DC current. If it's supposed to be a noise filter, the diode doesn't help, it hurts.

[a64pilot]

A diode also will cause a voltage drop I believe, can be used to trick an alternator into a slightly higher output.
Noise filters are I believe just capacitors, no diode.
This for example
http://www.aircraftspruce.com/catalo...lickkey=295439

[rwidman]

Originally Posted by Cheechako

Likely a diode which dis allows current to feed one direction. Usually for an alternator. I forget what the function is...

We can see that one of the components is a diode. It is too small of a diode to carry the charging current.

[Seawindii]

If it is a noise filter the information we have is incomplete. The cap would go in parallel between pos and neg leads -not in series. There would also be a little inductor in series with the pos lead. The diode is a mystery unless it's there as reverse polarity protection for some reason.

[Cheechako]

Originally Posted by rwidman

We can see that one of the components is a diode. It is too small of a diode to carry the charging current.

Yes, IIRC it can be to avoid the engine continuing to run with the key off on a gas engine. Or disallow current feeding back to... the gauges? after stopping the engine...? I should know by my mind not telling me.... Maybe keeps the regulator deactivated when not running..?

[a64pilot]

Originally Posted by rwidman

We can see that one of the components is a diode. It is too small of a diode to carry the charging current.

No, my understanding is it's used on the voltage sense line, the one that senses battery voltage, a diode will slightly drop that voltage, making the alt charge voltage increase to get to alternator set point.

Not saying that is what this is, but it's one use of a diode that is connected to an alternator

[four winds]

Certainly incomplete info.

Still curious which contact on the alt? And what about that other purple wire, factory wire?, Where does it go?

A "condenser" is commonly found in points distributors and on the back of many factory alternators, for noise suppression. As are resistor spark plugs. Many may recall a neighbor's lawn mower making noise in their car radio, no resistor plug or bad "open" condenser on the points.

However noise filters come in many configurations. Using diodes, resistors, inductors, transistors, etc. A band pass filter for example.

OP may have given up on us. And I don't have the answer. My curiosity waining.