Testing Diodes

[Bob_Roller]

I ran across a diode board that I removed from my Guzzi about a year ago, was having charge light issues .
Found my  charging troubleshooting guide from Motorrad Electric, tested  the diodes and all but one diode has 5-6 meg ( million ) ohms, one has .5 meg in both directions .
Would you consider this to be a not so healthy board ?
I still had the charge light issue after swapping the board with one from one of my R65's .

[montmil]

Although my electronical knowledge is limited, I thought diodes allowed current to flow in only one direction. If your diode is swinging both ways, that may not be a good thing.

[Bob_Roller]

I posted that wrong !!!!!
One direction, open, the other .5 meg .

[mrclubike]

Sounds bad to me

[Tony Smith]

I ran across a diode board that I removed from my Guzzi about a year ago, was having charge light issues .
Found my  charging troubleshooting guide from Motorrad Electric, tested  the diodes and all but one diode has 5-6 meg ( million ) ohms, one has .5 meg in both directions .
Would you consider this to be a not so healthy board ?
I still had the charge light issue after swapping the board with one from one of my R65's .

I'd say you have two faults.

If the Guzzi has the same arrangments as the BMW, the next step is to check your rotor and if that tests OK, check the stator.

[Bob_Roller]

I checked the rotor, brushes and stator and found no problems .
Found some questionable wiring connections ( previous owner ' modifications ' ) when I was rewiring the head light circuits and also found a few ground wires that were hidden out of sight, just happened to move the wire harness in that area and they popped out that may have helped as well .
Ran the engine with the bike in a darkened garage and didn't see the usual dimly lit charge light .
I need to get the bike out at night and see if the charge light is indeed not on .
I checked the voltage at the battery with the engine at 4200 rpm and I'm seeing 14.2 volts, the voltmeter on the bike shows the same reading, at best before, it was 13.2 volts, this is with minimal load on the electrical system, all of the lights off just the ignition being powered .
At the very least, it's better than it was before .

[Tony Smith]

I checked the voltage at the battery with the engine at 4200 rpm and I'm seeing 14.2 volts, the voltmeter on the bike shows the same reading, at best before, it was 13.2 volts, this is with minimal load on the electrical system, all of the lights off just the ignition being powered .

The rule of thumb I have always worked on is that anywhere between 13.8 and 14.5 immediately after startup means that the charging circuit is working. Turn your headlight on to high beam, stand on the brakes and put the blinkers on - if it doesn't drop below 13.8  you have an available "surplus" of power from the alternator.

In reference toy our earlier post - crook earths will do it every time, I simply assumed you had already dealt with that kind of thing.

[Justin B.]

On the one diode that reads the same in both directions see what else might be in the circuit with it.  A diode, when it goes bad, will usually be "open" in both directions or in rare instances shorted.