Recently purchased a 1995 268 Grady w/ Twin Johnson 175's.
Appears that neither engine is charging. I measured the impedance w/ a DVM (on Diode setting) of the rectifiers and found both to be damaged in my opinion:
STB: w/ neg lead of DVM on Red wire coming from rectifier, get conductance on both yellow wires from rectifier (w/ pos DVM on yellow wire), no conductance w/ leads reversed. Tach is NOT operational.
Port:
w/ neg lead of DVM on Red wire coming from rectifier, only get conductance on one yellow wire from rectifier (w/ pos DVM on yellow wire), no conductance w/ leads reversed. Tach appears to be operational.
QUESTION: is the base of the rectifier the "neg" side of the bridge? I believe the gray wire is for the Tach; not sure what the purple wire is for. I do not get any conductance w/ the neg lead of the DVM on the yellow wires from the rectifier the purple or gray wires or the base of the rectifier.
Please advise on my conclusion and the question re: the "neg" side of the bridge.
Yes using the diode test range of a digital multimeter with the rectifier/regulator completely disconnected measure between the red wire and each of the yellow wires. then reverse the meter connections and repeat. You should get lowish readings ( equal to the forward volts drop in mV) one way and high ( infinite ) readings the other way.
Now repeat all the above between the negative connection, a black wire if there is one , otherwise the metal case and the yellow wires
Any reading that does not fit with the high one way. low the other way indicates a failed rectifier diode.
(If you have an analog meter you can use a resistance range)
The purple wire is the voltage sensing connection but a replacement rectifier may not have this .... it will be done internally
The gray wire is the tachometer connection
A replacement may also have a black wire. If so ground it somewhere convenient .
More details in the CDI Electronics Troubleshooting guide
http://www.cdielectronics.com/wp-content/uploads/2013/02/CDI Troubleshooting Guide - 2012.pdf
BTW the details of the boat are irrelevant. If asking questions about an outboard engine always quote its full model number.
