Re: 93 johnson 30 elect. start not charging
Experience is that digital multimeters may or may not be OK for testing diodes using their Ohms ranges. Some seem to do it OK on some ranges others are no good on all ranges. Old fashioned analogue meters are OK.
I suspect the problem is that the digital meters apply a very small voltage which may not be high enough to for the diode to conduct in the forward direction. It takes about 0.7 volts to make a diode conduct. You would get a high resistance reading in both directions on all (6) diodes if that were the case.
Problem solved if the meter has a diode test range.
There are two bits of Joe's test procedure that I would not include if I was writing it. They are:
"then the red wire " in the first section
and the statement and "Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires" after the second section.
If of interest to you the lower diagram here
shows the circuit of a small four wire rectifier. The procedure basically tests the resistance of each of the 6 diodes in both forward and reverse directions. They should all have a low resistance in one direction and and infinite resistance in the other.
I reckon that your rectifier is blown and that your tachometer is getting its power from the battery and therefore continues to work.
When you get a new rectifier take care that you never connect the battery the wrong way round as that will blow the diodes in an instant. Disconnecting the battery while the engine is running may do so also.(BTW if it has 3 plain yellow leads without blue or gray stripes dont worry as it does not matter which of the yellows is which)
