Rectifier question on a 1994 mercury 90 hp

Little Richard

Petty Officer 3rd Class
Joined
Jun 9, 2017
Messages
78
Just bought a this boat. Noticed no increase in voltage on gauge while driving. Tested rectifier with voltmeter in diode mode. A few failed as well as it has a clear see thru bottom and it's fried. It has 2 yellows, 2 reds and grey wire. There is a black wire coming from power pack area and grounding to bolt on rectifier. I ordered a rectifier off e-bay that says it replaces part number 815279-3 but it has 6 wires coming out of rectifier. All the same except a black wire coming out of it too. Is this black wire a ground that I should just bolt down with other ground coming from power pack area.
 

Little Richard

Petty Officer 3rd Class
Joined
Jun 9, 2017
Messages
78
So I finally get this after market rectifier put it on. Tac was working off and on. But it was charging. Go to lake and run it notice tac not working check the rectifier temp with hand and it's hot. So I unplug gray wire but didn't have much time left on lake it seemed to cool down some. So I'm not really concerned with tac working or not. Could there be some issue with tac or something funny with how it's all wired up underneath the console causing these issues
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
LR, Usually the tach connects to the stator side of the rectifier and uses the pulses to convert to RPMs. So I can't see the tach causing the heat issues with your rectifier. However, the rectifier can get hot when you are running because it has a few amps flowing through it. So you may need to install an aluminum plate behind the rectifier to dissipate the heat build up, with some heat transferring grease compound as well. That should solve the rectifier heat issues. As for the tach, if the stator is working, and you have the tach connected up properly, and it still isn't working, you could have wiring problem or the tach itself is bad. JMHO
 
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