Electrical System Diagnosis Tips
Bottom line up front: when testing the rectifier output, you need a good battery installed to get accurate readings.
I'm posting my experience in hopes the next guy can learn from this, although I'm sure some on this forum have already come to the same conclusion.
So, I've been working on a 92 King Quad 300 that I bought used, and she's coming along. One issue I had was the electrical system. When I bought it, the battery was dead. I decided on a 20 year old quad that I probably won't be taking anywhere far from the house, that I was willing to replace the battery, but if the rest of the electrical system was toast, it wasn't worth the money to fix. I wanted to make sure the rest of the system would actually charge the battery before I spent the cash on one.
So, I started testing everything in the electrical system sequentially. The spark side of the magneto was fine, as was evident by the fact that I had good spark and all the resistance readings matched up.
Onto the charging side of the magneto, the coils tested fine on resistance, and the output voltage was over 55V AC (within specs). So, This led me to think one thing: the rectifier is the last possible problem. This assumption was compounded by the fact that my voltage output at the battery terminals was only 3-4V (with a dead battery installed).
I tested the resistance of the various terminals on the rectifier, as stated in the suzuki service manual, but, with an ordinary multimeter instead of the "suzuki pocket tester". And, as the manual says, the readings wont match up unless you use suzuki's tester. The rectifier is probably a pretty non-linear circuit, so this was of no use.
With the low voltage output of the rectifier, i was about ready to give up until I borrowed a buddy's battery on a hunch and plugged it in...the battery ready 12.5V before plugging it in, and the system was putting out 13.5V, so charging just fine. Lights worked fine, and then I took the quad out and ran it for a while, charged up ok.
So, without a good battery in the system, the rectifier output voltage will not be a good indicator of whether it's good or not. If i'd have known that, i'd have just borrowed a good battery first and checked the voltage output before i got so deep into testing the rest of this.
Hope this helps someone,