Electrical systems on these old outboards is still a mystery to me and I try to take every chance I can to learn about them. From my layman’s understanding of what you have described, I would take my test light clip to pos.+ on battery, battery neg- to ground on motor, then check for continuity at the yellow terminals on rectifier? Like I said, I’m not that familiar with electronics. If this is incorrect, please advise.
Thanks,
Jeff
Well then pay attention and learn something. But first, like I said, I don’t know about Mercury, but I presume that is a full wave bridge selenium rectifier. Nevertheless, the basics apply.
Picture 1 shows what is called a Full Wave Bridge Rectifier, Negative Ground. Very common. Understand this one and you can understand the variations. Note there are four diodes. The four diodes are connected to ground and battery + as shown. We are going to focus on only one diode at a time, first one marked D1 (by me, not on the actual unit)
Those four diodes must be tested one at a time. Any diode is tested the same way, regardless of where it is being used. So, look at picture 2 and learn how a diode is tested. Note the multimeter + and – leads are connected to each end of the diode. You will get either a high or low reading on the meter. Then the + and – leads are reversed in picture 2 (actually the diode is turned end for end). Again, you will get either a high or low reading on the meter. Conclusion: If you get a high reading on one test and a low reading on the second test, the diode is good..
Again, there are two tests for each diode and four diodes. You must test all four diodes. That is eight tests. It must pass all eight or the rectifier is junk. If you have not done all eight tests, you have not tested it at all.
And remember, disconnect the leads from the rectifier before beginning the tests. Otherwise you will get false results.
