Re: '88 60hp Johnson Charging system
You measure between the red and a yellow. You then swap the meter leads and measure again. One way you should get infinity but the other way you should get a low reading. If you don't get this difference the rectifier is bad. You move on to measure between the red and the other yellow. You should like wise get an infinite reading one way and a low reading the other way.
Then repeat between the case and each of the yellows. Each time you should get infinity one way and a low reading the other way. If you don't get those two readings anywhere the rectifier is bad.
All the low readings should be similar if they are not then something is wrong with it.
Each pair of readings is testing one of the four diodes. They all must conduct one way, giving the low reading, but not the other way.
Most likely if any of the diodes are bad you will get infinity both ways.
Heck its 02:40 in the morning here and I'm explaining how to test rectifiers. I'm off to bed!