2001 75hp 4 stroke Merc - charging issues

[Bananas Welcome]

Hi all,

I recently re-wired my boat, in the process I added a second battery, I have an older starting battery and brand new deep cycle on a 1-2-both switch with my outboard on the common post. After a week of fishing I noticed my voltage output was low with my outboard running (did not start the week this way, happened on day 4). With my start battery at 12.4, I started the outboard and the voltage was down around 12.2, it would then slowly creep up while underway to about 12.7/12.8. On the deep cycle, voltage was starting at 12.7, then would creep up to 13.5 or so. I assume I have a bad regulator. I switched batteries a couple times with the motor running during the week, NEVER through the OFF position, always through BOTH on the switch. But nonetheless I suspect this may have damaged the regulator.

I tested the stator and rectifier/regulator with a multimeter and it all checked out per the service manual, but I'm still suspect. I was going to order a new rectifier but I noticed the new version doesn't have tach output, and that it requires purchase of an updated engine wiring harness to get the sending lead for the tach. Does anyone know where the new harness is picking up the tach signal from? Any work arounds to avoid purchasing a $350 wiring harness on top of a $175 rectifier?

Any help would be appreciated!

Thanks

 

[Bananas Welcome]

Bump for views! Any help would be appreciated!

Thanks

 

[Texasmark]

Sounds to me like your rectifier/regulator is working. Might have your engine battery load tested for a dead cell....could be a cheap, easy solution if it fails. The deep cycle is telling you that the regulator has the capability to charge a battery, and your DC is probably a Group 27 and the starting battery a Group 24, with the DC having the larger capacity rating due to it's size meaning it is putting the larger load on the charging circuit, yet reaches the desired battery voltage.