70 HP Mercury won't run with rectifier connected to battery

[Mercerman]

1978 70hp Mercury lost spark. I started testing and found the rectifier was bad and have spark and runs good with rectifier removed. I did the continuity test on it and it shows as being bad. I got a new one and now it will run with the 2 yellow wires from stator connected (which it wouldn't do with the old rectifier) but it loses spark with the 12 volt wire connected. I did the continuity test on the new rectifier and it test out as good. When running with 12v wire off I checked rectifier 12v post for power and does not show any DC power but it does show some AC power. Is the new rectifier bad? Is the any other tests I can do?

 

[Reelrazor]

1978 70hp Mercury lost spark. I started testing and found the rectifier was bad and have spark and runs good with rectifier removed. I did the continuity test on it and it shows as being bad. I got a new one and now it will run with the 2 yellow wires from stator connected (which it wouldn't do with the old rectifier) but it loses spark with the 12 volt wire connected. I did the continuity test on the new rectifier and it test out as good. When running with 12v wire off I checked rectifier 12v post for power and does not show any DC power but it does show some AC power. Is the new rectifier bad? Is the any other tests I can do?

If AC is coming thru on the output (DC) post, then yes, the rectifier is bad.

 

[dingbat]

What are you calling a “continuity” test?

How did you determine that there was an AC component in the output?

Have you tested the stator to see if it’s not the root cause of the problem?

 

[Chris1956]

As soon as you connect the stator wires to the rectifier without the ground and/or charging wire, and start the motor, it will blow the rectifier. So don't do that.

if you read AC on the DC side of the rectifier, the rectifier is bad. if the stator is shorted to ground, thru the rectifier, the rectifier is bad.

 

[Faztbullet]

Make sure wires on correct posts of rectifier

 

[444]

As soon as you connect the stator wires to the rectifier without the ground and/or charging wire, and start the motor, it will blow the rectifier. So don't do that.

if you read AC on the DC side of the rectifier, the rectifier is bad. if the stator is shorted to ground, thru the rectifier, the rectifier is bad.

Yes. These rectifiers are super easy to fry. If you don't have all wires hooked up correctly and the battery connected you will kill it. First do all the checks on your stator to make sure it's good because a bad stator will also fry rectifiers.